Rainwater Harvesting

Cardew

Jon_Tiffany wrote: »

Darkpool is correct, the vast majority of houses discharge rainwater into the sewers. Its only on newer houses that the rain water is kept seperate.

I think there is some confusion between foul sewers and water drainage sewers. The latter not taking the rainwater to sewage treatment plants.

http://www.parliament.uk/documents/post/postpn289.pdf

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[FONT=NewsGothBT,Bold]Urban drainage[/FONT]

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The conventional way of dealing with rainfall and waste
water in urban areas has been to carry it away as quickly
as possible via underground pipes and sewers. Older (pre
1940s) areas normally have a combined sewer system,
where rainfall drains into sewers carrying foul water and
both are transferred to sewage treatment works.
Most newer developments have separate sewer systems:
water from gutters and roads is carried to soakaways,
through pipes to the nearest watercourse, but often
simply joins a combined sewer. Foul water travels by foul
sewer either directly to a sewage treatment works, or also
connects to the existing combined sewer network.
Most modern drainage systems are designed to cope with
rainfall events that occur with a one in thirty year
probability. Older parts of the system may be operating to
a lower standard. It is inevitable that the capacities of
sewers, covered urban water courses and other piped

systems will sometimes be exceeded.

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darkpool

About a hundred years rainwater and foul water all went to into one big drainage system and it was discharged untreated into the sea/ rivers. Then as attitudes changed it was thought it better to treat this water before discharge. Engineers then though it better to seperate the clean rainwater as it doesn't really need treated. So they started building drainage systems for roads etc. Rainwater falling on houses still went into sewers.

Then in the last 15 years it was thought better to seperate all rainwater (including rain falling on roofs) away from the foul water.

I can assure the reader that the vast majority of houses in the UK dischage roof water into the sewerage network.

"Most newer developments have separate sewer systems:
water from gutters and roads is carried to soakaways,
through pipes to the nearest watercourse, but often
simply joins a combined sewer." ehhmmm yes some of us have been saying that all along.

darkpool

"Most modern drainage systems are designed to cope with
rainfall events that occur with a one in thirty year
probability."

Yes they "cope" by discharging untreated sewage into the sea and rivers through combined sewer overflows during heavy rainfall.

I enclose a pic below of a CSO.

veryintrigued

Sorry to take thread off the original tack but....

I have a waterbutt which collects water from a shed roof. This is there more to do with the fact that this part of the garden used to get very wet.

Am thinking of using the collected water to flush loos (manually via a bucket - especially the downstairs one) rather than periodically emptying the butt down the outside drain.

Any thoughts anyone please? Does anyone do similar? If they do does the water stain the toilet? Smell? etc etc

Cheers all in advance

zeupater

darkpool wrote: »

About a hundred years rainwater and foul water all went to into one big drainage system and it was discharged untreated into the sea/ rivers. Then as attitudes changed it was thought it better to treat this water before discharge. Engineers then though it better to seperate the clean rainwater as it doesn't really need treated. So they started building drainage systems for roads etc. Rainwater falling on houses still went into sewers.

Then in the last 15 years it was thought better to seperate all rainwater (including rain falling on roofs) away from the foul water.

I can assure the reader that the vast majority of houses in the UK dischage roof water into the sewerage network.

"Most newer developments have separate sewer systems:
water from gutters and roads is carried to soakaways,
through pipes to the nearest watercourse, but often
simply joins a combined sewer." ehhmmm yes some of us have been saying that all along.

Hi All

Well, what an interesting debate, one which makes sense from one POV but is almost totally rediculous from another.

Firstly, looking at the postulation that it's only in the last 15 years that surface and foul water sewerage has been separated, well Cardew has posted Government sourced information stating otherwise and I'll agree. My house is almost 30 years old and is connected to separate systems as do almost every other household in the area which I live, and that includes a 500 year old Grade II listed house about 300 metres away. It is therefore highly likely that a much greater proportion of the housing stock than those completed in the last 15 years are connected to the two drainage systems.

Lets now look at the amount of water which falls on a roof and is discharged against what is made use of. It has been stated that the average rainfall is between 1m & 2m per year, however according to the Hadley centre the average is around 925mm, so let's settle on a rounded 1m, so we have an immediate potential 50% reduction of the problem in terms of m3 of water to be disposed of. My roof covers an area in the range of 200sqm, therefore about 200,000 litres of water falls on it every year, the equivalent of more than 60 toilet flushes per day. It is evident that in my case, having a rainwater harvesting system which could provide all of the toilet flush water throughout the year (without mains water suppliment) would use 15% to 20% of the potential available, so 80% to 85% would immediately go to the surface water drainage, the rest eventually to the foul water system ..... in a situation where there was no surface water drain 100% would go to the foul water system.

The example given above is based on a continuous rain which is not the case. Rain is intermittent, so in times of excess any normal storage system will fill and overflow, whilst in periods of drought the system will need mains water top-up anyway.

Storage requirement ? .... well if you had 1000litres of rainwater storage with a decent management system you might have a 8 to 10(ish) day buffer without rain before the system would call for a mains top-up. I don't see many rainwater harvesting systems being capable of storing a tonne of water.

With a large roof area I looked at a rainwater harvesting system but decided that the 'green' installers were simply on the 'get rich quick bandwagon' supplying underspecified/undersized systems at overinflated prices, therefore the only way to retro-install on a sensible basis would be on a DIY basis.

In summary, if you install a decently sized system on a DIY basis or it's included on a new build, and you're on a water meter .... go for it .... you'll save money & stop the water companies making so much profit if that's what you want to do, but you'll probably be doing very little to save the environment.

HTH
Z

Cardew

zeupater wrote: »

Hi All


Firstly, looking at the postulation that it's only in the last 15 years that surface and foul water sewerage has been separated, well Cardew has posted Government sourced information stating otherwise and I'll agree. My house is almost 30 years old and is connected to separate systems as do almost every other household in the area which I live, and that includes a 500 year old Grade II listed house about 300 metres away. It is therefore highly likely that a much greater proportion of the housing stock than those completed in the last 15 years are connected to the two drainage systems.

Z

My pal's father has owned a building firm, although he has now retired. Since this thread started I asked him about surface water drainage.

He started work in the building trade in the 1950s and he told me he has never been involved with a building where surface water entered the foul water sewer. That ties in with the Government report that it was pre-1940s.

[Deleted User]

darkpool wrote: »

Most rain that falls on roofs will enter the sewerage network.
QUOTE]

completely wrong darkpool, you obviously don`t know your buiding regs

darkpool

it's good to see some debate on the issue.

veryintigued, i see no real problem with using a bucket of rainwater to flush the toilet, but it sounds a lot of effort!

zeupater, i agree roughly with your calcs. i would say that most people in the UK don't have a 200m2 house though. Also rainwater can be used for otherthings apart from flushing toilets. other things you can use rainwater for include laundry, garden, washing cars etc. so the % of water used should be higher than 15%. I have to say that rainwater systems can store a lot more than 1 tonne of water.

I think some people are getting confused about road, foul and surface drainage. I enclose an extract from the Chartered Institution of Water and Environmental Managers. I think those boffins know more about it than some guy down the pub.

"Stormwater runoff from urban roofs makes a significant contribution to sewerage-derived flooding
and urban water quality problems. In most developed cities, roofs account for approximately 40-
50% of the impermeable urban surface area"

the info presented by cardew states quite clearly that modern houses also drain to combined sewers.

"Most newer developments have separate sewer systems:
water from gutters and roads is carried to soakaways,
through pipes to the nearest watercourse, but often
simply joins a combined sewer."

Rodders57

Rainwater harvesting is not new, it works if designed and installed right, its got nothing to do with the green bridgade or tree huggers. It helps reduce the impact a development has on the surrounding area. Most drains are combined, the water company dont want additional storm water over loading sewers that are already under pressure, for obvious reasons. Do you really need potable water of drinking quality to flush a toilet? Why are people so negative. Read the code for sustainability that developers have to abide by it might make sense.

Cardew

darkpool wrote: »

it's good to see some debate on the issue.

veryintigued, i see no real problem with using a bucket of rainwater to flush the toilet, but it sounds a lot of effort!

zeupater, i agree roughly with your calcs. i would say that most people in the UK don't have a 200m2 house though. Also rainwater can be used for otherthings apart from flushing toilets. other things you can use rainwater for include laundry, garden, washing cars etc. so the % of water used should be higher than 15%. I have to say that rainwater systems can store a lot more than 1 tonne of water.

I think some people are getting confused about road, foul and surface drainage. I enclose an extract from the Chartered Institution of Water and Environmental Managers. I think those boffins know more about it than some guy down the pub.

"Stormwater runoff from urban roofs makes a significant contribution to sewerage-derived flooding
and urban water quality problems. In most developed cities, roofs account for approximately 40-
50% of the impermeable urban surface area"

the info presented by cardew states quite clearly that modern houses also drain to combined sewers.

"Most newer developments have separate sewer systems:
water from gutters and roads is carried to soakaways,
through pipes to the nearest watercourse, but often
simply joins a combined sewer."

You seem to be quoting items out of context and changing your argument.

1. 'Developed Cities' 'Storm water' in the first quote.

Nobody is disputing that when there is a storm and billions of litres of water have to be drained, there is a problem with sewers.

However you are advancing the theory that using some rainwater to flush toilets is the solution to those problems.

2. the second quote states they have separate sewer systems and gives 3 methods of disposal for rainwater. A. to soakaways. B. through pipes to the nearest watercourse. C. but often joins a combined sewer.

However again the problems occur when there is heavy rainfall(storms) and I really can't see the logic that rainwater flushing the toilet is the answer to any problems.

The advantage of Rainwater harvesting is that you are not flushing drinking quality water down the drain. This reduces the load on water treatment plants and of course reduces your bill if metered!

However you are still using the foul sewer to dispose of that water whether it comes from the gutters or the mains water.