The main idea here is to install a very small tank in the roof to collect rain-water. This is used as required to flush the toilet.

This would conserve water - as typically, all rain water hitting the roof is currently wasted. Also, since this water often goes to the sewer directly, this reduces the size of the surge it experiences after heavy rain.

The tank need not be enormous, although ideally it would be able to provide several flushes after filling. Therefore there need not be any major structural implications.

Obviously, there must be a fall-back to the standard water supply when the tank is empty. This would not be difficult to arrange.

The micro-reservoir itself would be within the house, insulated from freezing and completely dark. Water would be delivered from the drain-pipe via a mesh and U-bend to protect it from debris. Ideally the U-bend would flush itself somehow when the tank was full, however I'm not sure how this would be done.

In rainy weather such as the UK winter the tank may rarely empty, so would provide an almost continuous benefit, particularly to those with metered water. As in the UK the main reservoirs are not currently filling over-winter, micro-reservoirs, if widely installed, would reduce some of the strain on the system. Rain-water is clean enough for this usage directly. This method also reduces the amount of water purified to drinking standard so provides an energy saving.

The system is intended to be cheap and easy to retrofit to an existing house. This would mean people might actually do it, while they generally have not taken other water conservation methods.
-- Loris, Jul 27 2006

Only a few thousand years old. http://en.wikipedia.org/wiki/Cistern
[ldischler, Jul 27 2006]

Collecting rainwater of the roof! What a novel idea!
-- DrCurry, Jul 27 2006


Genius I know... but the idea struck me as a bit different from the typical water-the-garden usage (which only very few people do anyway).
-- Loris, Jul 27 2006


... Come on ldishler, that is unfair. The idea may include a cistern, but the idea is clearly about the specific use and integration.

If you are wondering, I didn't use the word 'cistern' because a) then people would get confused with the toilet's own cistern, and b) I forgot it.
-- Loris, Jul 27 2006


In Jamaica it is called a *catchment tank*. I love their English.
-- xandram, Jul 27 2006


I saw a thing about it on Discovery. Widely used in Carribean homes, not only for flushing toilets but for drinking water as well. They are typically made of concrete and painted with a waterproof paint. They are scrubbed and cleaned a few times a year to prevent algae buildup. Not sure what difference there is in your idea.
-- fredberg, Jul 27 2006


The difference would be that this is a minor contribution to the water shortage, retro-fitted to the (eg UK) water distribution system at minimal cost, rather than the main water source.

I was thinking that this would be a relatively cheap, efficient point on the scale that people might be persuaded to do on economic as well as environmental grounds.
I certainly wasn't thinking that no-one in the world had ever thought of collecting water before, which is what people seem to be reading it as.
-- Loris, Jul 27 2006


I don't know if you know this [Loris], but people have been collecting water in cisterns for home use for years. Just thought I'd let you know that water collecting (like what your idea is about) is done, people do it all the time. Collecting water, that is. };-)
-- NotTheSharpestSpoon, Jul 27 2006


Thanks, NTSS, I now see the error of my ways. :)

Perhaps if you are not in the UK you don't realise the situation here. Britain gets more rain than many countries put together. In spite of this, every summer for the last few years there has been a water shortage. Virtually everybody gets all their water for drinking, bathing and watering the garden or farm from centralised reservoirs, after purification to drinkable standard. It might sound like madness, but this system worked quite well for a long time.

After a series of relatively dry years and increasing demand, however, the reservoir cachement areas are not sufficient. Rivers are being drained. Bans on the use of water for some purposes. The introduction of mandatory fitting of meters for what used to be un-metered.

Why rely on large reservoirs? Well, the rainfall patterns are perhaps different to Jamaica. Maybe there the rain there is more regular, so a relatively small tank will suffice to cover the occasional dry patch. In any case, we are now in a situation where very few houses can be converted to have large tanks with self-sufficient amounts of water. People are too lazy to go that route anyway. So we can't go the whole hog, but doing it in a small, easy way is still an option which could make a significant contribution.
-- Loris, Jul 27 2006


If memory serves, my parents have installed seven water-butts, used mainly for watering the garden. They are fed from the house roof, the green-house and a shed, and include a massive bespoke metal 3x3x1 metre tank. In summer one is connected to take the gray-water from the bath. There is no financial benefit, because they have an un-metered contract.

Yes, they have a large garden, my mother being a keen gardener. In summer they soon empty, because there isn't enough rain. In winter they rapidly over-flow.

Just thought you might want to know that.
-- Loris, Jul 27 2006


Ha!
From today's TV guide:

7:35 30 Minutes
Where has all the water gone? As water company profits soar, the programme asks why Britain can't seem to manage its water supply.
-- Loris, Jul 28 2006


Since there are no springs, rivers or streams in Bermuda, the entire island relies on catching and storing rainfall. Every house catches its own rainwater on its roof, and pipes it down into an underground tank. The water from there is then pumped around the house for showering, flushing, washing up and drinking. It's an incredibly efficient system that could, with a bit of forethought from the planners, certainly become viable in areas with high levels of rainfall.
-- zen_tom, Jul 28 2006


Sigh.

Sorry about the in-line links, I've included them just to cite my sources; couldn't be bothered putting them as real links.

Annual rainfall for England (long term average) 823 mm.
http://www.defra.gov.uk/ environment/statistics/ inlwater/iwrainfall.htm#iwtb1

Population density England 383/km^2
http://www.woodlands-junior. kent.sch.uk/customs/ questions/population.html

BUT population density (2001 census) London 4539/km^2; population density Birmingham 3452/km^2 (derived data from -) http://www.woodlands-junior. kent.sch.uk/customs/ questions/population/ cities.htm (Birmingham has a lot of large parks, London has fewer)

meaning approx 222 m^2 per person in London. If that were all used to catch rain, 182 m^3 water per person. Realistically, a fair proportion even of London is road, garden or park.

Current usage is 157 litres per person per day.
http://www.devon.gov.uk/ drought.pdf
Or ~57 m^3/year.

So even London could in theory collect enough rain, if all the rain was used just for domestic use. But it doesn't. (In the UK overall only 20% is domestic ( http://www.statistics.gov.uk/ cci/nugget.asp?id=159) But lets assume there are no other drains in London.

So why not? Well, as I've said before, most of the rain falls in the winter. So you'd need to collect and store, say, 40 m^3 per person to have a good chance of not running out over summer, if people used it as they do at the moment.
Bearing in mind that people are not distributed evenly - a more realistic figure is 4 or more people in a house with a footprint of, say, 10 by 20 metres (figure made up), and collection of 228 m^3 from 165 m^3 of rain per annum isn't possible, even if we could find a place to store 160 m^3 of water. It certainly couldn't be stored in the roof without extensive structural modifications!
The other issue is one of cleanliness. Centralised water purification is what people are now used to.

"Jamaica’s mean annual point rainfall varies from about 762 millimetres in coastal regions of both the north and south to over 7,620 millimetres in the Blue Mountains."...
p26, http://www.unccd.int/ actionprogrammes/lac/ national/2002/jamaica-eng.pdf

And the population density is almost exactly that for the UK as a whole, 244 per km^2: http://www.photius.com/ wfb1999/rankings/ population_density_2.html

I don't know how these people are arranged, but I'm willing to bet that: their houses have a larger surface area, and/or they live in the wetter region, and also possibly the rain is more predictable. Also as has been stated, the catchment tanks are below ground and the water is pumped. This is clearly a disadvantage.

So, frankly, if you want to make people in Britain collect all the water they use from their roof like they do in Jamaica then post that as a half-baked idea yourself. I believe my proposal has the advantages of being feasible, relatively easy to retrofit to the existing infrastructure, and hence infinitely more likely to be taken up by the public.

Move over, Vernon.
-- Loris, Aug 02 2006


My parents (who live in the UK) have a tank which collects rainwater from their roof, and then pipes it to their toilet cisterns and other greywater appliances for use in the home. Theirs is buried in the garden, as it's quite large.

As you admit that your parents have also done similar stuff, what is the novelty here? Using it as drinking water?

Incidentally, putting the tank in the roof is tricky, as that's where the water is coming from and your tank level will be above the drain level, so you'll need a pump, too. And a reservoir below it to ensure the pump has enough water to run sensibly.
-- moomintroll, Aug 02 2006


//the programme asks why Britain can't seem to manage its water supply.//

Well thats easy, because they are always drinking tea. ;p
-- jhomrighaus, Aug 02 2006


//My parents (who live in the UK) have a tank which collects rainwater from their roof, and then pipes it to their toilet cisterns and other greywater appliances for use in the home.//...
Interesting. If it is a commercial kit then my idea is baked.

...//Theirs is buried in the garden, as it's quite large.//
Ah, a difference then.

//As you admit that your parents have also done similar stuff, what is the novelty here?//
No, I said my parents had lots of water-butts to water the garden with. The point was that I'm aware that water can be collected from rooftops - my suggestion is a specific implementation, which I believe has advantages.

//Using it as drinking water?//
Oh, RTFI.

//Incidentally, putting the tank in the roof is tricky, as that's where the water is coming from and your tank level will be above the drain level, so you'll need a pump, too. And a reservoir below it to ensure the pump has enough water to run sensibly.//
I don't think so. A gutter above the top level of the water-tank would be fine. This might have to be installed above the bottom/outside edge of the sloping roof in some houses, but many have shapes making this unnecessary. Remember, it isn't to collect all the water potentially possible - because the reservoir isn't big enough to make it worthwhile. It can't be, because it mustn't be too heavy.
A primary goal of this design is to be very cheap to install on existing houses. Certainly one can have larger systems to collect more water. These are clearly baked in Jamaica and by your parents. But these are more expensive precisely because the increase in size means it can't be stored in the roof - which means a significant increase in cost and installing hassle due to the complexity of pumping the stuff to where it is needed. And thus, very few people in the UK have them.
-- Loris, Aug 03 2006



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