Monday, October 01, 2007

How should we manage water use in the home?

The more I learn about the Code for Sustainable Homes, the more uncomfortable I get. I mentioned that I had been in on an interesting seminar last week, on the water use guidelines set out in the Code, and this week I investigated a little further, armed with an Excel spreadsheet.

Water use is one of two mandatory aspects of the Code (the other being energy use). Mandatory, in this instance, means that you have to meet certain targets as regards notional water use in order for the house to gain a particular Code Level. It’s no good building a zero carbon house if it fails to meet the water use standards as well.

The target water usage levels that the Code demands go like this:
• Levels 1 and 2: theoretical 120 litres/person/day
• Levels 3 and 4: theoretical 105 litres/person/day
• Levels 5 and 6: theoretical 80 litres/person/day

Now I guess many people have read the code and noticed these figures and probably thought very little more about them. I certainly hadn’t until I sat in on this seminar last week. Until then, they were just numbers jumping at me off the page: they didn’t relate to anything or any actions. But my eyes have been opened and what I am now seeing is a little disturbing.

The point is that it doesn’t matter how much water you actually use, the Code judges everything by Mr and Mrs Average, Joe and Joanna public, and according to water company statistics, they use about 130lts per day each. They break it down thus:

• They each flush the loo 4.8 times a day (c 20lts)
• They wash their hands or brush their teeth for 40 seconds a day (10lts)
• They use about 25 lts at the kitchen sink each day
• Their washing machines account for 16lts per day each (49 lts per cycle, and J&J each use it once every three days)
• Their dishwasher uses another 4lts per day each
• And then there’s showering and bathing. It gets complex here because Jo likes showers and Joanna likes baths, but overall it evens out and tends to account for 50lts per day each
• I make that 125lts a day each. Give or take 5 lts, that’s it.
• This might have been better with a pie chart, but it wouldn’t have been so much fun.

The standards set out in the Code would seem to indicate implicitly that this amount of water usage (i.e. 130lts per person per day) is unsustainable — i.e. wicked and to be strongly discouraged. The challenge set out in the Code is not to change the washing or bathing habits of Joe and Joanna, but rather to engineer in solutions which enable them to live exactly as they do now whilst consuming much less piped water.

Welcome to the world of water-efficient appliances. Low flush toilets help matters, and that without any apparent pain. If you can specify aerated taps on the kitchen sink and a water-efficient washing machine you can rapidly reduce that notional figure of 130 lts per person per day down to just over 100 lts per day. So far so good. Just as with energy efficiency measures, the first steps are easy and cost effective. So you can get to Code Level 4 without too much hassle.

It’s that 80 litres a day at Level 5 and 6 which is the problem. You see there just don’t exist any water efficient products that can get Joe and Joanna’s usage down to such a low notional figure. That’s where my spreadsheet came in: I was tinkering with all the very low water usage appliances out there and I still couldn’t get below 102 lts per person per day. This includes:

• dual flush toilets that work on 4.5 lts full and 3 lts half flush
• showers that use just 7 lts per minute
• aerated kitchen taps using 2.5 lts per minute
• washing machines using 35 lts per cycle rather than 49 lts

So how do you go that extra mile, or in this case 22 lts, and get the notional consumption down to Code Level 5 and 6 requirements? The answer the Code is steering us towards is, of course, recycling, either via rainwater harvesting or grey water systems. But even by taking this big leap, you are not guaranteed a result. This is because Joe and Joanna, even with the most water efficient appliances installed in their home, are still using more than 80 lts a day before so much as a loo is flushed. Grey water systems, which reuse bath, shower and basin water for toilet flushing purposes, aren’t going to get you under the 80lts per person per day figure on their own. Rainwater harvesting systems can be set up to run washing machines as well as flush toilets and so in theory could get your notional usage figure down below 80lts per person per day, but only if they operate at near 100% efficiency which is unlikely over the course of a year — in prolonged periods without rain, the storage tanks empty and the systems switch over to tap water.

The conclusion has to be that this 80lts per person per day figure is really at the limits of what is technically possible at the moment. It may well be that you have to fit both a grey water and a rainwater recycling system to meet the target. Grey water systems seem to cost anywhere between £1500 and £2000, rainwater rather more. That’s not a problem if you are building exemplar homes for demonstration purposes but remember we are aiming this at every new home built after 2016. That is a phenomenal challenge and a phenomenal expense to be borne.

There are some further strange anomalies in how the guidance has been put together. If you specify a bidet, you take an instant 5lt per person per day penalty; if you specify a water softener, you take a 12.5lt per person per day penalty. It’s hard to see how anyone will be able to fit these into a new home and still make Code Level 6. On the other hand, if you specify a swimming pool or an outdoor whirlpool bath, there is no penalty at all!

Rather than tinkering about with how we distribute water around the home, wouldn’t it be a lot easier and a lot less hassle just to charge the correct price for tap water in the first place? All new homes in England have metered supplies now in any event, so we already have a perfectly responsive mechanism in place for restricting water usage. As has been pointed out elsewhere, there are many parts of the country where water shortage is not and is never likely to be an issue. Shouldn’t the water restriction measures in the Code reflect this?

Underlying this is a debate very similar to the one raging over renewable energy. The government seems to be keen to promote onsite renewable energy (also via the Code) despite all the evidence being that it is much cheaper and more efficient to green the National Grid. With water, there is no national water grid but coincidentally, there is an article in this week’s Building by David Lush arguing that there should be. The main argument used against building a national water distribution system is cost and Lush quotes an Environment Agency consultation paper suggesting that it would cost between £9billion and £15billion. That may sound like a lot, but £2,500 spent on water reduction measures in every house after 2016 would cost £625million a year and would end up surpassing the cost of building a national water grid after 20 years. Neither option is exactly cheap. It may be that we should do both: I am not against recycling grey water or rainwater, but I do worry about the Code’s insistence that we must keep putting more and more stuff into our homes in order to make them sustainable. Stuff not only costs, but it breaks down, it needs servicing. Its all very well enthusiasts fitting stuff, but 250,000 homes a year? Has anyone seriously thought through the implications?


Anonymous Anonymous said...

Discussions I've had suggest that CSH levels 5-6 for water are unachievable; I don't even know whether my house will achieve it. Moreover, because rainwater and greywater treatment usually use *more energy* than mains water treatment and pumping, they actually make climate change worse (consult Australian govt. websites for more on this). Oh dear.

Living in the Welsh Water area, which has a major water surplus, I wonder why if there's a short-term shortage W.W. don't fill tankers with water, sail them around the coast and sell the water to Thames or SE Water. Sea freight is very, very energy-efficient so this might use no more energy than pumping it through pipes (has anyone checked?). The revenue would certainly reduce my water bill!

In the long run, why not require all developers of a new house or flat to pay to retrofit two or three old homes with water-efficient appliances? Done abroad many times; never mentioned in the UK as far as I know.


5:34 pm  
Anonymous Anonymous said...


Just thought you might like to know how we save on water.
A combi boiler shower in the morning.
Whilst the water heats up we use this to fill a watering can. This water is used to do washing up/kettle boiling etc. All the waste shower water is used to flush the loo. Easily achieving 50 litres per person per day.

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Anonymous Anonymous said...

'How' & with what do you capture (harvest) this water - a bucket ?

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