Author Topic: Domestic Water Consumption  (Read 16163 times)

Mark Siddall

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Domestic Water Consumption
« on: April 24, 2007, 07:49:46 AM »
The average domestic water consumption is considered to be 160 litres per average person per day. The Code for Sustainable Home looks for a reduction in predicted water consumption to 80 litres a day. Furthermore it states: -

"This could be achieved by fitting such items as:
• 6/4 Dual Flush WC;
• Flow Reducing/Aerating taps throughout;
• 6-9 litres per minute shower (note that an average electric shower is about 6/7 litres per minute);
• a smaller, shaped bath – still long enough to lie down in, but less water required to fill it to a level consistent with personal comfort;
• 18ltr maximum volume dishwasher;
• 60ltr maximum volume washing machine.
To achieve the standard would also mean that about 30% of the water requirement of the home was provided from non-potable sources such as rainwater harvesting systems or grey water recycling systems."

Despite the fact that I now have a range of water saving technologies to hand I don't know whether they are really going to deliver the required savings. Why? To date I haven't seen any explanation of how to calculate these reductions (either specific to the CSH or in general). Can anyone offer some direction on how to make a suitable (reliable?) estimate for reductions in water consumption?

Thanks
Mark
« Last Edit: April 24, 2007, 09:41:18 AM by Mark Siddall »

Nick Grant

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Re: Domestic Water Consumption
« Reply #1 on: April 24, 2007, 04:07:57 PM »
Hi Mark

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.

Da Da

79.6642 l/p.day


« Last Edit: April 24, 2007, 06:06:23 PM by Nick Grant »

Mark Siddall

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Re: Domestic Water Consumption
« Reply #2 on: April 24, 2007, 11:55:30 PM »
Thanks Nick. Also good to know that the 80lts can be surpassed with a little input from the occupants. ;-)

Taps: I question the CSH's need for all taps to be spray/aerated taps, isn't is better to run a bath on full bore (reduce heat loss)? ....admittedly this is less about water conservation and more about energy but we have to think about the whole picture right? (Similar thing for the kitchen sink)

With regard to dead legs what max length would you suggest (I'm working on 5m at the moment but think that this could be overly generous. What do you think?)

Mark
« Last Edit: April 24, 2007, 11:57:54 PM by Mark Siddall »

Nick Grant

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Re: Domestic Water Consumption
« Reply #3 on: April 25, 2007, 06:56:15 AM »
Bath taps obviously shouldn't be spray and no credits for that. I meant sink and basins.

Re dead legs depends on pipe bore.

Attached screen shot from something I'm writing. 1.5 litres max was suggested by John Willoughby for EST advanced standard. The 30 seconds to run hot is supposed to be from Defra but I cant find ref.

Obviously the shorter the better. We have 13m of 10mm pex to remote bathroom basin with Tapmagic spray and it's acceptable. Kitchen tap is about 5m of 10mm pex and runs hot almost immediately.

The volumes assume plug flow but that's close enough as a guide.

Nigel Bishton

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Re: Domestic Water Consumption
« Reply #4 on: April 25, 2007, 04:58:50 PM »
I have been advised by a consultant not to use spray taps as they would have to be sterilised monthly to satisfy the ACOP on legionella.

Anyone else had any experience of this and what would be the alternative?

Nick Grant

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Re: Domestic Water Consumption
« Reply #5 on: April 25, 2007, 10:00:41 PM »
I'd be very interested to hear their reasoning. Why would bugs living on a spray fitting be more dangerous than those living on any other tap outlet. Is you consultant worried about aerosols? If so I'd argue that a regulated spray (1.7 l/min) will give less aerosol than an unregulated splashy tap.

Nick

Nigel Bishton

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Re: Domestic Water Consumption
« Reply #6 on: April 27, 2007, 09:41:59 AM »
I'd be very interested to hear their reasoning. Why would bugs living on a spray fitting be more dangerous than those living on any other tap outlet. Is you consultant worried about aerosols? If so I'd argue that a regulated spray (1.7 l/min) will give less aerosol than an unregulated splashy tap.

Nick

I understand that there are two issues, build up of scale which harbours legionella and secondly the aerosol issue with the taps. Shower heads require an even more vigorous maintenance programme.

The monthly cleaning is mainly descaling.
Nigel

Nick Grant

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Re: Domestic Water Consumption
« Reply #7 on: June 27, 2007, 09:17:23 PM »
Starting to look as the CSH again and just put our own house into the BRE Water calculator. Some of what follows is a repeat of previous posts, the trumpet blowing is for dramatic effect, bear with me.

Water saving is my thing, I'm a water saving anorak. We built the house around the compost loo and there is a leak free 4 litre Ifö ES4 WC in the bathroom. We have microbore pipe to everything except the bath so taps run hot or cold with minimum waste.

The bath is of modest capacity and only used as a treat but can fit 2 at a squeeze.

The wash basin has a special tap with eco-brake ceramic cartridge and a Tapmagic outlet which can give a spray or full flow. The shower head has been changed perhaps 10 times in search of the ultimate water saving shower that will still be acceptable to guests. We don't have a dishwasher and our washing machine was purchased after writing a paper on the subject. You get the gist, I've looked into this, my holiday snaps are of toilets, it's what I do for a living.

Not surprisingly our water bills are very modest and we average a tad under 50 litres per person for 2 people despite clean bodies, clothes and dishes.

So how many points do we get out of 5?

A grand total of nil point and a predicted 122 litres/person.day

Guess I'd better find another line of work pretty sharpish...

Nick

J Ingram

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Re: Domestic Water Consumption
« Reply #8 on: June 28, 2007, 09:02:06 PM »
On  flow restrictor/aerators, as your suppose to fit isolator valves on all
outlets , taps etc
all I do is adjust them down , reducing tsshe flow ,hopefully reducing the amount of water going down the drain, since plug seem to be going out of fashion

is there a potential negative doing this ?


We stayed with some friend a while ago and I used a dishwasher for the first time
Buy them time I'd unloaded and load up the thing I could have washed the stuff twice over in a bowl and had them back in the cupboard , unless your into catering I cant see the point ( I have a family of 5)

Jim


Nick Grant

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Re: Domestic Water Consumption
« Reply #9 on: July 02, 2007, 12:12:42 PM »
Nigel

Your idea is free and OK but not as good as actual regulators which ensure constant flow rate regardless of pressure. for example I have in the past set the flow to spray taps in a washroom. However when more than one tap is on the pressure can drop and so the flow reduces from optimum to a dribble. Also someone will come along and adjust it.

So fine at home but for new build and commercial go for regulated aerators or sprays - assuming mains pressure.

Mark Moodie

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Re: Domestic Water Consumption
« Reply #10 on: July 03, 2007, 10:05:34 PM »
Like Nick, water efficiency is my business and we also went to great lengths to achieve very low water use and carbon neutrality and achieved 50 l/p.day for a family of 4 with 2 small kids. The BRE water calculator predicts 138.57 (!) litres/p and zero points.

J Ingram

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Re: Domestic Water Consumption
« Reply #11 on: July 13, 2007, 10:23:03 AM »
Nick

Your points make sense, I'm keen to reduce my consumption
so it works well in my own situation.
but I can see the potential problems when you give people the
option to fiddle with things


thanks

Jim

Nick Grant

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Re: Domestic Water Consumption
« Reply #12 on: July 13, 2007, 01:48:06 PM »
In what way Jim?

J Ingram

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Re: Domestic Water Consumption
« Reply #13 on: July 16, 2007, 11:04:49 PM »
Nick
I meant if you give some people the option to turn things up they might

so as you suggested fitting aerator/flow restrictor in new build and commercial
is the more sensible idea rather than using isolating valve to reduce the flow,
which I thought might be a simple alternative , as I do at home

cheers Jim
 

Mark Siddall

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Re: Domestic Water Consumption
« Reply #14 on: October 08, 2007, 06:09:19 PM »
Nick,
So, now that a revised CSH Tech Guide is available (October 2007 edition)has it resolved the problems with the water use cals?

Mark

 

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