Archive for the ‘Water’ Category
Cath Hassell, ech2o consultants www.ech2o.co.uk
We all know the high environmental load of traditional swimming pools; the energy required to heat them; the chlorine required to keep them clean; the large amount of water that is required to fill them in the first place and refill them after they have been drained down for the winter. It’s also common knowledge that a designer can ensure a pool is more sustainable by specifying a pool cover, installing solar thermal panels to heat the pool and considering ozone instead of chlorine as the disinfection method. But all of that does not need to concern us in the environmental building sector because if a client wants a pool, there is a perfect solution available on the market and that is a natural swimming pool. Right? Well wrong actually!
I was recently asked to provide a critical analysis of the water strategy for a large multi-million pound dwelling that, as with many such sustainable properties, had not addressed water beyond rainwater harvesting and dual flush loos. On first reading the one thing we didn’t have to worry about was the swimming pool as it was going to be a natural pool. But when we began to analyse the pool specification in detail some worrying facts emerged.
Natural swimming pools
A natural pool consists of a swimming area and a planted area, (the filtration zone). The plants extract any nutrients that run into the water, thus restricting the growth of algae. A pump is used to circulate the water through a filter to aid cleaning. Natural swimming pools have several environmental advantages; no chemicals are required to clean the pool, thus preventing the formation of hazardous chemicals; they do not require draining down over the winter and refilling in the summer, thus saving water; they use less energy as they are not heated; they provide a habitat for insects and amphibians in the shallow planted zone; and birds use the pool for drinking and bathing.
Natural pools are often designed to be larger than a traditional pool; in this case a surface area of 124m2 (compared to an average traditional pool size of 45m2). You would assume that a natural swimming pool would be quite happy (indeed prefer) to be filled with alternative sources of water to mains water. However, when we asked about filling the pool from the commercial fish ponds on the site we were told the nutrient levels in the water would be too high. So this pool would require 153m3 of mains water to fill – the equivalent of a daily use of 420 litres of water for a whole year! We asked about topping up with rainwater from the green roof and were again told that nutrient levels would be too high even though no fertiliser would be used on the roof.
Evaporation, even from an unheated pool, is significant. Calculating evaporation rates is complicated, with many variables. The main factors that affect evaporation rates from domestic outdoor pools are pool surface area, temperature difference between the water and air, humidity levels and wind. Research in Australia has shown that the average daily evaporation rates from an unheated pool are 6.4 mm/day (6.4 litres/m2/day) for the six hottest months in Melbourne. The same research shows that a pool in Perth, in the coldest months, loses 3,000 litres a month over a surface area of 42m2. In the absence of any comparable data for the UK I calculated evaporation rates from the pond using both sets of data (with changes to better reflect UK conditions) and came up with some depressing figures. With a pool surface area of 124m2, and a rate of 2.1mm evaporation a day, 260 litres a day is lost to evaporation (against the average water use in the UK of 150 litres/person/day. Over four months this is 31,200 litres (31m3). Adding evaporation across the remaining eight months of the year (albeit at a lesser rate) total yearly losses are over a third of the pool volume. So far, so bad, and it gets worse… To keep the pool clear the water is continuously pumped through a filter. A pool this size will require a pump drawing 400 Watts. That is 3,504Wh of electricity a year, the average household’s total electricity use!
So am I saying no ponds at all? No, of course not. That would make for very poor garden design. But these highly engineered natural pools are not the solution. On this site, the response by the architects to our findings was swift and decisive. They reduced the size of the pool to 45m2 for the swimming area with a planting zone of 12m2, cutting evaporation rates, original fill water and electrical load by over 50%. And although the natural pool is currently still in the specification, the architects agreed to our suggestion to provide a natural pond as well, filled and topped up with rainwater from the green roof. The level of the pond will rise and fall with the seasons and the available rainfall. Any overflow from the pond will drain naturally into the ground via swales and rain gardens. A natural pond increases the biodiversity on this site as well as providing another focal point, and uses the runoff from the roof in the best possible way.
 The size of the planted area depends on the pool type but most have a planting zone of between 15-25% of the surface area of the pool.
 Chlorine in pool water reacts with organic compounds in the water such as sweat and urine to produce a host of hazardous chemical compounds that include nitrogen trichloride, aldehydes
 Both of the main suppliers of natural pools in the UK stated this.
 As Melbourne in the summer is hotter than the UK, I used a figure of one third the evaporation rates (i.e. 2.1mm/day) and over four months rather than six months. Using the Perth data as it stands but for all twelve months, yearly evaporation losses would be 36m3.
Cath Hassell ech2o consultants www.ech2o.co.uk
Team GB delivered during the Olympic Games on their medal target, but what about water use? Does the claim of “the greenest games ever” hold up under scrutiny? The goal was a 40% water saving compared to 2006 industry standards, and although the “industry standards” were not explicitly stated it was an ambitious target that, if achieved, would certainly be impressive. When the Olympic Park Water Strategy report stated that: “…the Park in legacy mode is expected to exceed this target with a total 57% saving in water consumption”, you could almost feel the nation’s chests swell with pride. However, just as the mantra “delivered on time and on budget” falls apart when you realise that the budget for the Games was increased to £9 billion from the original £2.4 billion, predictions of reduced water consumption also need to be analysed more closely.
The 40% target
In 2006, WC flush was 6 litres maximum, urinal controls were mandatory, and taps in public washrooms were already time controlled, so a 40% reduction would require alternative sources of water as well as efficient appliances, and originally it was expected that would be mostly from rainwater harvesting. The preferred specification for appliances was 4.5 litres single flush WC, fan assisted waterless urinals, PIR operated taps at 5 litres/minute and showers at 9 litres/minute. All venues installed low flush toilets, and low flow showers and taps as recommended in the design brief, but the Velodrome and Aquatics Centre opted for flushing urinals. The Velodrome and Handball Arena installed rainwater harvesting and the Aquatics Centre installed backwash recycling. Rainwater harvesting is estimated to reduce the Velodrome’s potable water demand by 20% and predicted to generate a potable water saving of 530m3 a year. (However, with just 25m3 of storage and the fact that the stadium will be used so intermittently after the Games, this figure seems optimistic to me.) Recycling the filter backwash water for WC and urinal flushing is estimated to reduce water consumption in the Aquatics Centre by three per cent.
Where was the water used?
It was estimated that water consumption up to and during the Games would be 361 Mega litres (Ml). Post Games the figure is 5,735 Ml over the remaining 24 years design life. This meant that 6% of total lifetime water use would be during the Games. How that requirement for water was broken down is very interesting. I had assumed the greatest demand would be WC and urinal flushing from the estimated 3.7 million visitors, closely followed by the Aquatics Centre. But in fact, the Olympic Park Water Strategy estimated water consumption to be as follows: the Combined Cooling, Heating and Power Plant at 26.9%, Eton Manor at 15.6%, 7.7% for the Aquatics Centre and 7.5% for establishment irrigation leaving just 14.5% of water requirement for the remaining venues on the site which included the 80,000 capacity Olympic Stadium and the Press Centre.
I hadn’t even considered the process water requirement for the CCHP plant, but it made sense once highlighted. But Eton Manor, what was happening there? And why was so much water required for irrigation when most of the park was planted with wildflower meadows?
Water based hockey pitch
Hockey is played at Eton Manor on a water based pitch. Water-based synthetic turfs enable the ball to be transferred more quickly than sand-based surfaces and are less abrasive so reduce friction burns, but require a lot of water as the pitch is flooded with water before the start of every match to a depth of 3mm. With a playing surface of approximately 6,000 m², and top up required at half time, water use averages 26 m³ per match. Added to this is the fact that the pitch has to be kept wet constantly and, to prevent the growth of algae, hydrogen peroxide is added to the water. As the Intentional Hockey Federation themselves (back in 2006) suggested that hybrid pitches (sand and water based) would be preferable because of the very high water consumption of water based pitches, it is a pity that a hybrid pitch was not specified for the 2012 Games.
I was surprised at such a high requirement for irrigation. The wildlife meadows on the Park require establishment irrigation for two seasons, (which is not the case in other projects I have been involved with) whilst the trees require irrigation for the first three to four years. Initially, consideration was given to constructing swales to store rainwater but this solution was rejected because “they could not hold the volumes of water required”. So, all irrigation uses water from the Old Ford Water Recycling Treatment Works. There are a lot of green walls around the park which require permanent irrigation, and although drip irrigation is the preferred delivery method throughout the Park for all the planting, using an industry standard approach is a missed opportunity. If the irrigation system was combined with soil moisture sensors then at least the unprecedented rains would have reduced the requirement for watering.
And the result is…
There are no figures to back up the 57% claim, so we will disqualify it. For the 40% target, 18% is estimated to be met by water efficient appliances and the remaining 22% by Old Ford using treated sewage from the northern outflow sewer. Old Ford will provide a minimum 46 Ml (46,000m3) of treated water a year, and as the first direct reuse of waste water in the UK, it will be interesting to see how it performs, particularly in regard to the amount of energy it uses per m3 of water supplied. Water consumption on site during the construction phase seems to have been ignored which (if that is the case) is a cop out. So certainly not a gold medal, but as the feel good factor is still in the air I shall go for bronze.
This article was first published in Green Building magazine, Autumn 2012
 One Mega litre is 1,000,000 litres or 1,000m3
 5,735Ml over 24 years is an average of 239 Ml a year. I assume that the bulk of it will be for the CCHP plant and the 2,818 new homes that will be built on the site, although no details were given in the report.
 The Olympics Village is not classified as being part of the Park.
 Though if the CCHP plant and Eaton Manor hockey park are taken out of the equation, the reduction from water efficient appliances increases to 33%.
Alex Stephenson Director, UK Stormwater Division, Hydro International. www.engineeringnaturesway.co.uk
With one voice, a cry for ‘clarity, clarity, clarity’ has gone out to Government in response to the National SuDS Standards consultation. There are strong indications that both local government and industry believe the standards, as they currently stand, are not yet fit for purpose.
The devil is definitely in the detail as far as the new standards are concerned: The problem is – no-one is quite sure what the detail is. Many are worried that a dilution of the original principles has crept in, introducing exemptions in a number of areas which could undermine the whole intent.
What’s more, just when everyone should be gearing up for an October 2012 start, everything seems to have gone quiet at Defra. No doubt, the responses will have given the Government much food for thought.
So here’s my best guess at the top seven big questions on Defra’s ‘to do’ list.
1. What Will the Guidelines Contain?
The Government has promised detailed Guidelines to accompany the National Standards. There’s little doubt that the Standards in their current form are insufficient without them. As the Local Government Association (LGA) attests, the standards are more ‘a set of guiding principles’ than a ‘national standard or specification’. Many agree the guidelines would need to have been written, scrutinised and agreed by industry before the new SuDS approval system begins. To be effective, the guidance needs to be binding, not just advisory.
2. When will the new regulations commence?
Local Authorities have requested at least 6 months’ notice before commencement. This already takes us beyond October. One leading local authority respondent, the Cambridgeshire Flood Risk Management Partnership claims a 1st October start is “unrealistic” and “unlikely to be achievable” for many councils to build skills and capacity. It seems April 2013 is looking ever more likely – a route favoured by myself.
True, some local authorities are well advanced in their preparations and there is nothing to stop them and forward-looking developers from adhering to SuDs principles in the meantime – providing there is clarity on adoption of any SuDS features developed during the interim phases.
3. What will the Transitional arrangements be?
The Government’s suggestion of a phased implementation in which only developments over 10 dwellings will be required to have SuDS approval for the first 3 years has drawn mixed views. Phasing would allow lessons to be learned on larger schemes by developers and local authorities alike, but some feel this could water down and delay the national take-up of SuDS significantly, as many smaller developers are precisely those that require more guidance and support. One option would be for SABs to be able to sub-contract the necessary expertise from industry, where the skills already exist.
4. What does ‘affordable’ mean?
Affordability is the most hotly debated issue of all: The Government’s statement that “Drainage for surface runoff should be sustainable and affordable to build and maintain” may seem easy to agree with at first glance. But how will affordability be tested in practice?
Developers welcome the addition of an affordability test as part of the guidelines. But there are major disagreements on what affordability means: For developers it means that the cost of constructing SuDS should not outweigh the benefits, protecting them from unnecessary costs. But focusing on capital costs alone is not comparing like with like, and some fear affordability will be used as a ‘get out’ clause. Many argue that affordability should consider the holistic, whole-life benefits of a SuDS scheme. The multi-benefits of SuDs, such as amenity and biodiversity, could also be monetised in some way.
Incidentally, there is a strong argument that SuDS are cheaper or comparable to conventional systems, in any case. And what exactly is meant by conventional, by the way?
5. What does Reasonably Practicable Mean?
The term ‘reasonably practicable’ is used 15 times in the proposed standards. In a dispute between a developer and a SAB – who decides what that means exactly? Will the guidance be sufficient, or will it be left to lawyers to argue?
6. Where does the LA’s responsibility to adopt end, and the Water Company’s begin?
There appear to be some significant potential differences of interpretation of the definition of “sustainable drainage system” as “those parts of a drainage system not vested in a sewerage undertaker”. Respondents have demanded more clarity in terms of which parts of the drainage system will be adopted by the SAB and which part by the Water Company. The forthcoming publication of Sewers for Adoption 7th edition may be able to provide more guidance.
7. Why Exempt Single Properties from SuDS Approval?
The proposal that SuDS Approval and subsequent Local Authority adoption should only be required for drainage systems serving more property is a cause of inconsistency, if not confusion. Why should a large commercial scheme, such as a supermarket for example, not go through the SAB process? What about residential buildings in multiple occupation? Unadopted SuDS on these developments would have to be maintained by the tenants or building owners.
Runoff from large single properties could have significant impact on surface water drainage in the area. What recourse would the water company have in such circumstances? Surely a ruling based on minimum area of land would be more reasonable?
I must stress that there is overwhelming support for the Government in implementing the Flood and Water Management Act, and for the principles embodied in Schedule 3, which seeks to implement the National Standards.
Getting things right from the outset is so important, because failure will lead to a patchy and inconsistent implementation of SuDS across England and Wales. It’s been five years since widespread flooding in England set us on the road to radical changes in surface water management. We must neither falter, nor delay any further.
There was never really any doubt about the subject of this blog for me. It always had to be about “the wettest drought on record”. It is usually easier to get people to sign up to sustainable water during a drought, (although, conversely, it makes it harder as soon as the drought is over.) But this “drought” has proved far harder because of the amount of rainfall. Plus the fact that the south west of England and the Midlands were classified as being in drought even as the unprecedented April rains were falling made it even more of a PR disaster.
Definition of drought
So what exactly were the conditions that lead to the drought being announced? It was well documented that there had been below average winter rainfall over the last two winters leading to exceptionally low ground water levels. In addition, reservoir levels were low at a time when they needed to be full. In England and Walesit is the Environment Agency (EA) that decides when to call a drought, and it defines drought in two different ways. Environmental drought
is when a shortage of rainfall has a detrimental impact on the environment and water company supply drought
is when a shortage of rainfall causes concern for the ability of water companies to supply their customers. The EA makes a decision to move to drought status based on a series of factors including meteorological, hydrological, environmental, agricultural, and public supply.[i]
(I would also add political here but that is just my opinion.) The drought designated areas increased rapidly from the 12th
March until, by the 16th
April, over 75% of England was officially in drought; the subsequent sodden April and early May resulted in a lifting of formal drought status from many areas although the south east and east of England still officially remain in drought
How can we prevent further droughts?
This question is often posed, but it is not the question that needs to be asked. As we cannot control how much rain falls, we should be asking: “How do we manage our water supplies so that prolonged periods of below average rainfall do not result in a problem?” Obviously there are many solutions, from collecting rainwater, recycling greywater, reducing leakage (both in the mains and in customer’s branch pipes), retrofitting water efficient appliances and just using less! As these messages were drowned out (excuse the pun) by the call to transfer water from wetter to drier areas let’s look at how possible that would be.
Transferring water from Scotland to South East England
Areas of Scotland (e.g. the Highlands) do get a lot of water (up to 4000mm/year) but the east of Scotland gets no more than the east of England at 600mm/year. And, in 2010, when the east of Scotland experienced a drought, there was no transfer of water from the west to the east because (just as between Scotland and South East England) the infrastructure to provide large scale water transfer doesn’t exist, and the cost to build it is extremely high.[i]
For a pipeline to be built between Scotland or the north of England to the south east there needs to be a guaranteed profit to incentivise the billions of pounds worth of investment that is needed. A guaranteed profit requires a guaranteed demand. But since 2005 there have been just two hosepipe bans in the south east (and one in the north west!). if the pipeline had already been built, in six out of the last eight years there would have been no demand for this extra water. That is poor odds on which to invest so much money and it is unlikely the shareholders of a private water company would support such a decision. Nor, one would imagine, would the people of Scotland. Of course we can argue that climate change will lead to more likelihood of drought and maybe it will, but in fact, in the UK, wetter, rather than drier winters, are indicated on current climate change modelling. The solution is unworkable without major Government backing, and that will not happen however much local politicians in the south east want it to.
A smarter message
At the start of the hosepipe ban Thames Water flooded London with posters that read “There is a drought. Please save water
” splashed across a picture of cracked earth, which in reality, if not on the posters, quickly turned into a sea of mud. Eventually the sodden April weather resulted in a change to the message which now reads “Yes we know it’s been raining a lot recently but there are still water shortages.
” This is a far more useful message, and yet it still implies, that never mind, it will soon be over and then you can go back to using as much water as you want. We need to highlight a far smarter message.[ii]
It should be as follows: the UK requires a 14% reduction in water use down from 150 litres to 130 litres/person/day and that using water sustainably is something we should be doing all the time, across the whole of the UK, not just during a drought and not just in the south east.
This blog is an edited version of an article that will appear in the summer edition of Green Building Magazine
United Utilities have recently built a 35 mile long supply pipeline to link Liverpool and Manchester. it cost £125 million, £3.6 million per mile. And, as Panorama’s “Drinking our Rivers Dry? (http://www.bbc.co.uk/programmes/b013pzns
) showed, the Environment Agency and Thames Water are arguing (to the detriment of the River Kennet) over who should pay for a pipeline just a few miles long, precisely because of the cost of such a solution.
by Cath Hassell of ech2o consultants
I was in Delft recently with my partner where, as usual, we ordered tap water with our evening meal. It was pleasant enough, no discernable chlorine taste, but it certainly wasn’t worth the three Euros sixty that appeared on the bill! This slightly surreal experience was closely followed by a visit to Bruges where the restaurants and cafes refused point blank to serve tap water at all. So I decided to investigate the bottled water industry in more detail, and to ask whether we, as construction professionals, can reduce the amount of bottled water consumed in the UK.
Value of the bottled water market
It is an industry that has grown rapidly in the past 25 years, with global consumption in 2010 at 225 billion litres and a worldwide market worth £52 billion pounds a year.  It is a staggering fact that the world spends over six times as much per year on bottled water than it does on water supply and sanitation. Despite a slight downturn in sales in the last few years in the US (due to pressure from both environmentalists and municipal water suppliers) it is still the world’s fastest growing consumer beverage, and likely to remain so as increasing sales in China more than make up for any decrease in the States. Whilst consumption of bottled water per head in the UK is low compared to many European countries at 38 litres per head, it has also risen rapidly since the 1980’s. In 2009, 2.1 billion litres of bottled water were bought and the bottled water market in the UK is estimated to be worth between £1.4-2 billion.
The decline in drinking tap water
So why is the number of people drinking tap water in the UK declining? As with most countries it is due to three main factors: a fear about the quality of tap water, preferences of taste, and convenience.
We don’t need to drink bottled water in the UK because our tap water is unsafe; in fact, the tests that tap water is subjected to before it reaches our taps are more stringent than those required for bottled water. The “Story of Bottled Water” (from the same people that produced the “Story of Stuff”) and available at http://storyofstuff.org/bottledwater/ explains how the bottled water industry in the US systematically set out to persuade consumers that tap water was essentially unsafe, and did so very successfully. In the UK the British Soft Drinks Association has been accused of doing the same thing, though they have denied it.
The taste issue is more subjective. Certainly there are areas in the UK where tap water is heavily chlorinated and unpalatable. However, filtering the tap water or allowing it to stand before drinking solves that problem, both at a far lower monetary and environmental cost than drinking bottled water. Depending where in the UK you live, tap water costs between 0.2 and 0.5 p per litre directly from the tap. Filtering at point of use will double the price at worst.
The environmental impact of bottled water v tap water
There are several environmental issues that are of concern when bottled water replaces tap water. Excessive withdrawal of natural mineral or spring water to produce bottled water can threaten local streams and groundwater, transporting the water to the consumer results in a far higher carbon load than delivering to a tap; the manufacture and disposal of billions of plastic bottles causes pollution, litter and fills landfill sites.
The carbon load of mains water in the UK is, on average 0.35kg CO2 for every m3 of tap water delivered to the tap. Compare that to the carbon load of trucking bottles of water around the UK, a heavy and bulky commodity. To exacerbate the situation, of the 2.1 billion litres of water we drink every year, only 1.6 billion are UK-produced, meaning that 24% of the bottled water we consume in the UK is imported. Whilst most of our imported water is from France, bottled water from Turkey and Fiji and even bottled rainwater from Australia (Cloud Juice) is available in our shops.
To reduce bulk and weight most bottled water is now sold in plastic rather than glass bottles, which brings extra environmental problems. Most plastic water bottles are made from polyethylene terephthalate (PET), which is recyclable but research in the US has shown that less than 20% are recycled, with the bulk of the remainder going to landfill. Whilst figures are not easily available for the UK, the figures are likely to be similar. In both Sweden and Germany there is a substantial deposit on plastic bottles at point of sale and therefore recycling rates are far higher, but there seems little political will to introduce such a system in the UK in the near future. Because so much bottled water is consumed outside of the home environment, many empty bottles are disposed of in street bins where recycling rates are far lower than from home bins. Even recycling does not completely solve the problem as only 4% of PET bottles are recycled back into new bottles; most are merely downcycled.
At first sight this does not seem an issue that those of us who work in the building industry can affect. But when we design kitchens we can specify a separate filtered water tap outlet and in the commercial sector we can design in water fountains or space and water connections for chilled water units fed directly from the mains water supply.
 $100 billion a year to $15 billion a year
By Jim Allen | E&M West Ltd | www.eandmwest.co.uk
And yet here we are rushing towards 2012 with alarming rapidity. Remember the disastrous floods that overwhelmed parts of the South West in 2007, and Cumbria in 2009? As I write the rain is lashing the north again, last month it was Mevagissey, bringing back memories of Boscastle, shrinking the distance of time. Flooding is a direct cause of human misery, dislocation on a local and national scale, with a heavy cost directly to individuals, their insurers and the country as a whole.
The Pitt review in 2008 led directly to The Flood and Water Management Act 2010. This seeks to make management of flood risk a pro-active, rather than a reactive mopping up exercise. Local authorities are key to the brave new world it seeks to create, looking up towards the Environment Agency for a strategic framework, and outwards to drainage boards, water companies and the design community to create, implement and manage solutions on the ground. Management of surface water is the issue, and the adoption of sustainable drainage systems the key component.
All well and good, but over 3 years on from Pitt almost none of this is in place, and the current framework for enactment will not complete until the very end of 2014, over 3 years hence. So why the delay?
The Bill will impact on planning processes, with sustainable drainage solutions a requirement for all but the very smallest schemes. This at a time when one of the coalition’s much vaunted strategies for recovery is the abolition of red tape and reform of the planning processes.
Local authorities are the key to successful implementation, and while they have skilled engineers they are too few in number, and not always trained in the design of sustainable drainage schemes. Yet they are charged with establishing Sustainable Drainage Boards to sanction development and management of schemes and other assets post construction. They are not ready.
On the other side of the fence, sustainable drainage schemes, done well, use space that could be used to raise scheme density and payback for developers on their expensively acquired land-banks. Compliance will generate upfront costs and potentially delays. Government is desperately keen to raise new housing starts, and is looking at ways to incentivise rather than discourage development.
Perhaps no surprise then that implementation is so slow, although so far no one seems to be admitting to any dragging of the feet.
The design community must put the counter arguments as strongly as we can. We have a golden opportunity to use good design to improve amenity and biodiversity to the benefit of the wider community. Permeable paving has its place, but it’s not paving paradise. The existing system is broken, and is full of inconsistencies and hard to reconcile interests. Reform is essential if we are to move forward and make the right kind of investment, saving costs to the wider economy in future years.
The politicians would do well to remember the misery flooding creates. It’s twice this year residents in Mevagissey have mopped out their homes; they may not know much about the Water Bill 2010 but they will surely want to know why this is happening again.
by Cath Hassell of ech2o consultants
Language is important; it is one of the things that define us as human. As the environmental building industry expands, new systems, processes and products are introduced and new words start to become common currency. I am interested (and often surprised) by the way technical terms become misused by building professionals as well as the general public.
Rainwater and greywater
Rainwater and greywater (two completely different types of water, with differing requirements for treatment and storage) are increasingly referred to as greywater. So much so I now routinely ask whether the speaker really means greywater, regardless of the conviction with which they state the word. Rainwater is obviously rain that has fallen out of the sky, which in a conventional building is discharged to a surface water sewer, combined sewer, or a soakaway; if it is stored for use back in the building it is still rainwater, until it is used. Once it is used it becomes either foul water (if used to flush WCs or urinals) or waste water if used for washing clothes. If wastewater from a bath, basin or shower is collected for re-use it becomes greywater. If greywater is used to flush WCs it becomes foul water. If it is used in washing machines it becomes waste water (but would not circulate through the greywater recycling system again as waste water from washing machines has too many detergents in it to be considered as suitable for greywater recycling). Simples!
Greywater and “blackwater”
When I first heard the term greywater used for waste water (back in 1997) I naively assumed it to be a reference to the appearance of the water due to the effect of scum formation, and the colour wastewater becomes after it begins to biologically decompose. But then I started to hear the term “blackwater” to describe water from toilets. “Blackwater” categorically does not describe the appearance of foul water either in the sewers or whilst undergoing treatment at a sewage treatment plant. It is an example of using the term black to describe something that has negative connotations, rather than an actual description (such as blackboard). We have a perfectly adequate term to describe water from toilets, which is foul water, and in the 21st Century our language should be smarter than this.
Sewage treatment for direct or indirect re-use
Now the term “blackwater treatment”[i] is being used in the UK to describe the on-site treatment of sewage in an eco town or on an eco development, where the effluent is used back in the development for certain non-potable purposes. Although this is a different process to normal sewage treatment in so far as the sewage effluent is treated beyond normal secondary and tertiary treatment, (and the effluent may meet drinking water standards), the technology is not new, is not confined to just “eco” developments, and has a technical term that describes it perfectly, which is sewage treatment for direct re-use. In the US, home of the term “blackwater”[ii], such treatment and distribution schemes, of which there are an increasing number, are now being referred to as simply “water re-use” systems.
~ Direct re-use: the planned and deliberate use of treated sewage. At its most extreme, the sewage effluent is cleaned to potable water standard and injected directly into the mains supplying a town or city. However at present most direct re-use systems clean the sewage effluent so that it is considered fit for purpose for irrigation, WC flushing and urinal flushing, and supply a secondary network of distribution pipework for this water as well as a mains supply network. A separate distribution network is very costly. Therefore it makes economic sense for sewage treatment re-use to be directly into the mains. From 1985 to 1992 the City of Denver, USA, ran a large scale trial of direct re-use and found that water quality parameters were equal to or better than the city’s drinking water. However, public perception about direct re-use for potable water supplies is still mostly negative, and is holding back large scale take-up of this process.
~ Indirect re-use: water that is taken from a river, lake or aquifer that has received sewage or sewage effluent. Much of the water we use in our buildings in the UK could be classified as indirect re-use, i.e. effluent from one town’s sewage treatment plant is discharged into a river, taken out from the same river further downstream, to be cleaned and supplied to the next town. Hence the saying that every glass of water we drink has passed through seven other people’s kidneys first. With planned indirect water re-use the sewage effluent is discharged immediately upstream of the water treatment plant or used to recharge aquifers. Indirect re-use of sewage effluent is beginning to be used far more around the world as water demand increases and the water suppliers need a guaranteed supply.
In the UK the most high profile example of a sewage treatment plant with direct re-use is on the Olympic site. Whilst I have seen some publications refer to it by its technical term I have also seen it referred to as a “blackwater” sewage treatment facility and a “blackwater” treatment system. It is sewage treatment with direct re-use for non potable purposes. It is a highly technical solution; let’s call it by its correct technical name.
[i] The term isn’t even used correctly as “blackwater” treatment plants deal with both foul and waste water (i.e. “blackwater” and greywater).
[ii]The first reference I could find to it was in a US patent applied for in 1974 where water was divided into “white water” (drinking water) and “black water” (sewage from the building).
This article was first published in Green Building Magazine, Spring 2011.