All very depressing really. A CSH assessor called me this morning. Despite going to great lengths to design and build to best water efficiency practice he failed to achieve 1 credit on a project that was heading for EcoHomes excellent and AECB Silver standard for energy. The same water spec is delivering 50 l/p.day in at least 3 other dwellings with eco-aware owners but no hardship.
Terribly flawed model and concept.http://www.planningportal.gov.uk/uploads/code_for_sustainable_homes_techguide.pdf
Gives you what you need to make a spreadsheet (BRE one available to assessors but maths are the same)
1. assumes water use in sink and basins is directly proportional to flow rate. To get any sort of reduction you need 1.7 l/min sprays. For bathroom you could use Tap Magic which gives spray but opens up to fill a basin - this works OK but isn't regulated to 1.7 l/m. The report on meeting the code by WRc assumed 1.7 l/min sprays for kitchen tap. OK if you don't need to cook, wash up or make a cup of tea.
2. shower time assumed to be a fairly generous 5 mins so to get the volume down you need a pretty low flow shower head. Will this still be in place in a week's time after handover?
3. Bath to shower ratio fixed at 0.6 : 0.4 if both installed. If you want a modest bath that 2 can squeeze into once in a while but you usually shower, then say good bye to your points.
4. WCs improvement on Eco Homes. Delayed action inlet valves get a mention, no mention of how they or anything other than manufacturer's claimed flush volumes would get entered into the model. No points for leak detection or avoidance (siphon flush).
5. bidet assumed to increase water use if installed but I'd argue it can save water (top and tail rather than bath or shower every day).
6. no credit for minimising hot water dead legs and no penalties for combis that need a long warm up.
7. grey and rain is probably the only way to get the last few litres and so achieve <80 l/p.d theoretical, 2-3k+ to save about 20 l/p.d.
So I suggest do all the good stuff you know about and install spray taps all round @ £5 each, put plants in the bath or hide it under a table and fit a 6 l/min shower head.