Rainwater Harvesting

darkpool

But the BS standard for rainwater harvesting (8515) recomends a 2m3 storage tank for a 60m2 house with 4 occupants. This standard also recomends an additional 3.6m3 if stormwater control is to be considered. That means a 5.6m3 tank would be used.

Where are you getting the 1m3 tank size? It looks like you pulled the size from thin air? If someone goes to the expense of putting rainwater harvesting in do you think they will skimp on the tank size? I personally would think that a tank that would store at least a months water use would be right.

Why do you think a storm lasting several days leads to the most flooding in the sewerage network?

I'll agree that an above ground tank could have algae problems. However as long as the tank isn't translucent and has some insulation it should be ok.

So what do we all think about the new desalination plant in London? Does it not take over 7kWh to produce a 1000 litres of water? Would rainwater harvesting not reduce this energy use?

zeupater

darkpool wrote: »

But the BS standard for rainwater harvesting (8515) recomends a 2m3 storage tank for a 60m2 house with 4 occupants. This standard also recomends an additional 3.6m3 if stormwater control is to be considered. That means a 5.6m3 tank would be used.

Where are you getting the 1m3 tank size? It looks like you pulled the size from thin air? If someone goes to the expense of putting rainwater harvesting in do you think they will skimp on the tank size? I personally would think that a tank that would store at least a months water use would be right.

Why do you think a storm lasting several days leads to the most flooding in the sewerage network?

I'll agree that an above ground tank could have algae problems. However as long as the tank isn't translucent and has some insulation it should be ok.

So what do we all think about the new desalination plant in London? Does it not take over 7kWh to produce a 1000 litres of water? Would rainwater harvesting not reduce this energy use?

Hi

I don't really know where you're going on this thread, and why .... Firstly you mention that rainwater caused foul drain flooding, whereas it's only heavy downpour conditions which cause the problem. Drainage is designed to cope with all but 1 in x year conditions without overflowing. These include localised rainfall events at around or in excess of 1"/hour.

You menioned that only in the past 15 years have the surface and foul water systems have been separated, and that new housing stock is insignificant compared to the total housing stock, whereas both my house being 30 years old and other sources question this.

The position moved on to football grounds, supermarkets etc ... something which almost no-one on this forum has any direct say on, whereas some are interested in domestic rainwater harvesting. However, when it is pointed out that many factories, offices and retail developments already have SuDS you claim to have not seen any, despite designing some .... If you were into windsurfing I could show you at least three large SuDS which were constructed in the 70's which are now utilised as public amenities within 10 miles of where I live, and then visit a local supermarket with thousands of tonnes of surface water drainage buffering below it's car park, then a new public building project with solar thermal collection and storage, solar pv, passive space heating, rainwater harvesting, SuDS, GSHP with thermal storage recycling ... but that's nothing to do with anything which the majority of people can do, which is simple retro-fit systems.

You mention that storage systems don't need to be underground and that everything should be based on a 60sqm house, so allowing for an overground storage of 1mx1mx1m containing an unsupported 1 tonne of water with it's associated space requirements calculations to support previous figurs were made.

You claim that a harvesting system doesn't need to be pumped, however, with most properties in the UK having their toilet upstairs how would they use the water in the toilet apart from harvesting and storing directly into a loft tank.

Now, when the data doesn't suit, the conditions change to looking at design requirements for new developments, which is entirely in contradiction to your earlier position relating to the majority of the housing stock.

Do you seriously think that anyone would retro-fit a tank weighing two tonnes in a standard loft, or up to a 5 tonne flood control tank above ground in a retro-fit situation.

You started the thread on rainwater harvesting, then mentioned that rainwater harvesting would prevent flooding, now it's rainwater harvesting combined with domestic SuDs which would prevent flooding.

If you have anything to do with a rainwater harvesting systems supplier I think that you are putting at least one potential customer off doing anything at all, and I suspect that that is not what you are attempting to do. If you can supply relevant data based on realistic conditions you will likely get support, however, simply claiming that harvesting rainwater in normal rainfall conditions will stop foulwater flooding doesn't make any sense, as flooding occurs mainly in heavy continuous or exceptional rainfall conditions.

Z

[Deleted User]

Rodders57 wrote: »

So in your opinion a housing estate no matter how big or small has no impact on sewers or water supply or local environment. Back that up with figures. Retrorofit always costs more no matter what work you have done, its a no brainer. In ten years time it will be as common as solar pv or thermal on roofs. Sorry but you guys must get pleasure winding people up on here. Read the Code for sustainability, its here to stay and written in stone. The problem lies more with training personnel, we are 20 yrs behind Europe in that respect. Now there will be a blame Europe reaction

The one thing I would do without is rainwater harvesting. It involves a lot of groundworking, plastic and plumbing. The filters need cleaning, the toilet cisterns can leak because of small grit getting under the seal, the pump needs electricity and has to pump water from way below ground up to the highest toilet, so how efficient is that

Let us get the basics right in this country before highfalutin ideas from theorists, ie insulation plus water saving and energy saving

darkpool

zeupater wrote: »

Hi

I don't really know where you're going on this thread, and why .... Firstly you mention that rainwater caused foul drain flooding, whereas it's only heavy downpour conditions which cause the problem. Drainage is designed to cope with all but 1 in x year conditions without overflowing. These include localised rainfall events at around or in excess of 1"/hour.

You menioned that only in the past 15 years have the surface and foul water systems have been separated, and that new housing stock is insignificant compared to the total housing stock, whereas both my house being 30 years old and other sources question this.

The position moved on to football grounds, supermarkets etc ... something which almost no-one on this forum has any direct say on, whereas some are interested in domestic rainwater harvesting. However, when it is pointed out that many factories, offices and retail developments already have SuDS you claim to have not seen any, despite designing some .... If you were into windsurfing I could show you at least three large SuDS which were constructed in the 70's which are now utilised as public amenities within 10 miles of where I live, and then visit a local supermarket with thousands of tonnes of surface water drainage buffering below it's car park, then a new public building project with solar thermal collection and storage, solar pv, passive space heating, rainwater harvesting, SuDS, GSHP with thermal storage recycling ... but that's nothing to do with anything which the majority of people can do, which is simple retro-fit systems.

You mention that storage systems don't need to be underground and that everything should be based on a 60sqm house, so allowing for an overground storage of 1mx1mx1m containing an unsupported 1 tonne of water with it's associated space requirements calculations to support previous figurs were made.

You claim that a harvesting system doesn't need to be pumped, however, with most properties in the UK having their toilet upstairs how would they use the water in the toilet apart from harvesting and storing directly into a loft tank.

Now, when the data doesn't suit, the conditions change to looking at design requirements for new developments, which is entirely in contradiction to your earlier position relating to the majority of the housing stock.

Do you seriously think that anyone would retro-fit a tank weighing two tonnes in a standard loft, or up to a 5 tonne flood control tank above ground in a retro-fit situation.

You started the thread on rainwater harvesting, then mentioned that rainwater harvesting would prevent flooding, now it's rainwater harvesting combined with domestic SuDs which would prevent flooding.

If you have anything to do with a rainwater harvesting systems supplier I think that you are putting at least one potential customer off doing anything at all, and I suspect that that is not what you are attempting to do. If you can supply relevant data based on realistic conditions you will likely get support, however, simply claiming that harvesting rainwater in normal rainfall conditions will stop foulwater flooding doesn't make any sense, as flooding occurs mainly in heavy continuous or exceptional rainfall conditions.

Z

But the way many sewerage systems cope is by dumping untreated sewage into rivers/ streams. You think this is acceptable in the 21st century? You like windsurfing in raw sewage

I have my doubts you have a separate sewerage system. I think it more likely the water you see discharging into your brook is from the road drainage.

In a previous post you say there are many football grounds/ supermarket with suds. Then in this thread you say there are 5 within a 10 mile radius of you. So is it fair to say the vast majority of commercial buildings in your area have no suds at all?

I’ll admit spending thousands on retrofitting existing houses generally isn’t going to be worth it. But in certain situations it will be wise investment. It would need to be considered on a case by case basis. But I would have thought that was common sense? Just like saying solar panels aren’t suitable for every property.

Why do you think domestic systems should be limited to a 1m3 tank?

I think if you google the subject some more you will find that 15 to 30 minute storms cause most flooding in sewerage systems. M5-60 in this country is about 15 to 20mm. So a 5 year return period 15minute storm might be about 10mm. Why don’t you do your calcs again with 10mm and see what reduction you get

This is what the BS standard on rainwater harvesting says. Don’t get offended, but I put more weight in their word than yours.

On-site collection and use of rainwater is an alternative to public
mains water supply for a variety of non-potable water uses in the
home, workplace and garden. It can also provide benefits for theattenuation of surface water run-off.

[Deleted User]

darkpool, it is tarmac and concrete drives that you should be targeting if you are concerned about groundwater runoff and flooding. our house is sustainable (and tested) to the highest level and we are surrounded by gravel so that rainwater sinks into the ground and does no harm. You have an unsustainable and impractical, bee in your bonnet

darkpool

maybe you're right kittie. but do you think BS standards and CIWEM have a bee in their bonnet as well? Or perhaps they are intelligent people who have looked at the problem and decided attenuating rainfall from roofs will reduce flooding?

I think you are right about driveways by the way. Grasscrete or permeable blockwork is better than tarmac/ concrete

dave_ave

Great thread, so I thought I'd join in.

I harvest my rainwater to flush my downstairs toilet (the one most used for a quick no. 1;-). I'm on a water meter, so anything to save money. I got an IBC for free from my ex-wife's employer. It's 1 cu m in size, so holds 1,000 litres. I used some plastic 15mm pipe and installed a basic filter on the output. It used to sit on some 1m high scaffolding at the side of my house and collect rainwater from my semi detached roof, but I found I didn't use enough of the saved water for flushing and it constantly overflowed. I've since had an extension built and the IBC is now in my new brick shed, still on the scaffolding, but the pipe to the toilet is underground now. I only harvest the shed roof now (6 sq m) and it's more than enough for the family. In fact, the overflow from the IBC fills a water butt. The whole setup cost buttons to be honest. No pump needed as it all works on gravity.

Perhaps the debate on rainwater and foul water entering a common sewer depends on where you live? All the properties I have ever lived in (Cardiff) discharge everything into the sewer. I have looked at numerous drainage systems when having building work done and they all enter the sewer at the closest manhole, both foul and rainwater.

dave_ave

Oh forgot to mention, my employer, a rail operator in Cardiff, harvests rainwater from the roof of the depot where the trains are serviced. The roof has got to be the size of 3 football pitches. There are a dozen 6m high silos to store the water and it is pumped to clean the trains.

darkpool

thanks dave,

it's good to hear some evidence that installing a RH system doesn't cost the price of "brand new car". at the end of the day RH is not rocket science, it's collecting water in a tank - something man has been able to do for thousands of years.

it's also good to know that your employer managed to look at the costs and benefits of RH and decided it was worth it. i was looking at RH paybacks for a farm last night. a 10k investment in RH led to a 3k annual saving. i think that is a really good return.

zeupater

darkpool wrote: »

But the way many sewerage systems cope is by dumping untreated sewage into rivers/ streams. You think this is acceptable in the 21st century? You like windsurfing in raw sewage

I have my doubts you have a separate sewerage system. I think it more likely the water you see discharging into your brook is from the road drainage.

In a previous post you say there are many football grounds/ supermarket with suds. Then in this thread you say there are 5 within a 10 mile radius of you. So is it fair to say the vast majority of commercial buildings in your area have no suds at all?

I’ll admit spending thousands on retrofitting existing houses generally isn’t going to be worth it. But in certain situations it will be wise investment. It would need to be considered on a case by case basis. But I would have thought that was common sense? Just like saying solar panels aren’t suitable for every property.

Why do you think domestic systems should be limited to a 1m3 tank?

I think if you google the subject some more you will find that 15 to 30 minute storms cause most flooding in sewerage systems. M5-60 in this country is about 15 to 20mm. So a 5 year return period 15minute storm might be about 10mm. Why don’t you do your calcs again with 10mm and see what reduction you get

This is what the BS standard on rainwater harvesting says. Don’t get offended, but I put more weight in their word than yours.

On-site collection and use of rainwater is an alternative to public
mains water supply for a variety of non-potable water uses in the
home, workplace and garden. It can also provide benefits for theattenuation of surface water run-off.

Hi Darkpool

I'll address the points in order ...

No I don't think that it's acceptible to dump raw sewage, my position is simply related to the postulation that retro-fitted domestic rainwater harvesting systems will provide a significant benefit to the prevention of foul water drain flooding. As for windsurfing in raw sewage, I referred to SuDS which were built in the 1970s to specifically intercept and control surface water drainage for new housing, office & light industrial areas.

Regarding your personal doubts relating to my drainage being separate. I can assure you that they are. Both the surface water and foul water deep main drains pass below my front garden and both have access covers in my garden. On a regular basis they are inspected by the water company who, out of courtesy, knock on my front door prior to my joining them to look down a pair of exceptionally deep chambers. When they arrive they have drawings of the local drainage system in order to locate the access points & are happy to discuss the details of the system before spraying the tops of the access covers with different coloured paint to identify which is foul water & which is surface !!.

Regarding the five SuDS systems, they are simply five examples. I'll agree that not everywhere has SuDS systems, but in the area I live in they have been incorporated into developments in one form or another for at least 40 years. Most are of a size which are simply designed into a landscaped area as a seemingly natural water feature.

I agree that rainwater harvesting for domestic water use is an excellent idea and I have been/am considering it myself, as previously posted. My issue is simply with the separation of what a rainwater harvesting system is for & what a SuDS system is for and that retrofit domestic rainwater harvesting systems are ineffective at alleviating foul water drainage overflow.

Looking at the 1m3 tank. This is the second time you have asked this. As I have explained previously, I have received quotations for harvesting systems. The largest storage I was quoted on was for a 1100litre system, which would provide 8 to 10 days worth of storage at our usage, that particular installer claimed that was their most popular requirement and had therefore settled on it as effectively being almost a standard solution. I have explained that my belief was that a month of storage would be preferable and having available space I therefore based the calculations provided for my property on 3500litre storage. It is highy unlikely that most people who would install a system with a capacity of much over 1000litres due to space, asthetics and the complexities involved with anything larger. Dave_ave has recently posted he uses a 1000litre IBC (standard industrial storage/delivery container) raised on a tower as his solution, a great low cost solution, but thats a tonne on a tower, imagine the DIY engineering required for 2 tonnes, 3 tonnes, 5 tonnes or whatever would be required to create a combined harvesting/SuDs system and what the reaction would be when the DIY engineering for a massive system fails. 1cu m is the solution being offered up by professional installers, 1 cu m also seems to be the low cost DIY solution using IBCs too.

Regarding the rainfall. 11mm in one hour ?. I understand that you are looking at design specification rainfall events, but is that really what we are debating, I thought that your position on using rainwater harvesting systems as a buffer was in relation to exceptional events which, being outside the civil engineers design specification and brief actually cause the systems to fail. My position is not based on Google, it's based on the number of times you see/hear reports of a month of rainfall in a couple of days. You seem to be quoting design specifications and classifying the bodies which set the specifications as being correct in everything they do & claim, which, if this was true there would be no flood events anyway because the drainage systems would cope.

You're in Glasgow therefore I've just actually followed your advice and looked for Met-Office weather conditions for your area to see if the are substantially different from those in mine. The following is an quotation from their site on your area ....

'Periods of prolonged rainfall can lead to widespread flooding, especially in winter and early spring when soils are usually near saturation and snowmelt can be a contributing factor. An example was 10-11 December 1994 when a slow-moving frontal zone resulted in unusually high rainfall totals in the Glasgow-Irvine areas. For example, at Paisley, 88 mm was recorded on 10th with about 133 mm over the 2 days. Flooding occurred in the River Irvine catchment and there was disruption to rail travel in Glasgow. The highest Scottish daily rainfall total (238 mm) was recorded in the region at Sloy, Loch Lomond on 17 January 1974. This may be compared with the highest daily UK total of 279 mm recorded at Martinstown in Dorset on 18 July 1955.'
http://www.metoffice.gov.uk/climate/uk/ws/print.html

It is important to note that my calculations were all based on 83mm (1000/12) being a months rainfall and that this could fall in a couple of days and that a half full system is likely to overflow after 1/3"(8mm) of rainfall. The event above delivered more than the figure I used within half the time and 60% more in the same period. This was a flood event.

Finally, regarding the reference to the BS standard on rainwater harvesting. Of course, I agree with what they say, they are the experts and I am not. However, looking at what you have quoted, what does it really say in the text which you have highlighted ? ... "It can also provide benefits for theattenuation of surface water run-off" ... I agree, it will, but they have not quantified the benefit, whereas I have by roughly calculating a 6% benefit ..... are you able to provide a link to any peer reviewed study or any other source which provides a domestic rainwater harvesting system benefit on surface water drainage from a domestic property which results in a quantifiable percentage greater than 6% in flood causing rainfall conditions, ie a months rainfall in 2 days ?

Logic dictates that the available capacity of a system at any point in time is the difference between it's current level and it's maximum capacity and when any system is full it will overflow. Logic would also point towards overspecification on the capacity of rainwater harvesting systems relative to the domestic usage would simple result in the system operating at a higher average fill level, therefore having a 3.5 tonne or a 35 tonne harvesting system the availabe capacity at any point in time would be the same, that being the usage since the system was last full ..... Rainwater harvesting systems are not an effective solution to foul water drainage overflow.

Z