Rainwater Harvesting

zeupater

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."

Hi

I agree with your point that rainwater can be used for things other than flushing the toilets, however, in my case it really makes little difference. Let me explain .... our household appliances are all top notch high efficiency models, we wash the car rarely, but when we do it's with a bucket or a pressure washer & the garden is watered from a waterbutt. I would estimate that the total for all of the water used in these areas per week is the equivalent to a little over 1 day of toilet flushing. Apart from toilet flushing the only other major water usage is for hot water with mixed cold for personal hygene and this would equate to somewhere around 1/2 to 2/3 of the toilet flushed volume.

Regarding the storage of water, yes systems can store over 1 tonne of water, but most don't. When I looked into it the 'We're green and doing it for the planet not profit' installers all quoted for undersized systems, the largest being 1100litres, at prices which equated to a new small car. Let's quickly consider a system which could provide a months worth of storage, say 3.5 tonnes. It rains, it doesn't rain, it rains. My roof area would collect 5 tonnes of water for each 1" of rainfall, therefore to top up a half full system would require 1/3" (8mm) before the system overflows to the drainage system. In a storm event this would equate to filling the system well within within 15 minutes, after that the runoff would divert to standard drainage anyway, joining the water from my driveway (which covers an area as large as the house), the pavement, the road etc ...

I know where my surface water drains to, it's a brook a couple of hundred metres away, therefore, in my circumstances there is absolutely no risk of causing foul water overflow. However, in heavy rainfall or storm conditions, where many inches of water can fall within a short period, even a 3500 litre system would make little difference on what was dumped to drainage. Considering this, I see absolutely no advantage in installing a system on drainage based environmental grounds, but I would still consider having a DIY system from a moneysaving view ... after all, this is a moneysaving website

Z

Applebob

Manchester should harvest their water! : )

darkpool

zeupater, yes i agree from the sounds of it rainwater harvesting wouldn't make much difference/ any difference to flooding from sewers for your house.

But there will be houses/ businesses where rainwater harvesting will make a significant difference to overflowing sewers and raw sewage being discharged into streams.

For instance how about a football stadium? It's got a very large roof and a high demand for water to irrigate the grass and flush toilets.

regarding the cost of rainwater harvesting, it sounds like you were looking at a 'Rolls Royce' scheme. at it's most basic rainwater harvesting is a £20 water butt from B and Q.

cardew, the majority of houses in the UK have a combined sewer. so using rainwater to flush toilets etc will reduce water going into the sewerage system. this is because you are reducing the amount of mains water you are flushing down the toilet. i'm not saying rainwater harvesting will stop sewer flooding but it will certainly help.

Cardew

darkpool wrote: »

cardew, the majority of houses in the UK have a combined sewer. so using rainwater to flush toilets etc will reduce water going into the sewerage system. this is because you are reducing the amount of mains water you are flushing down the toilet. i'm not saying rainwater harvesting will stop sewer flooding but it will certainly help.

I am certainly not arguing against rainwater harvesting - except the cost of retrofit systems for toilets etc is a joke in Money Saving terms.

It is these statements of yours that make no sense IMO.

Perhaps the main environmental benefit of rainwater harvesting is that it means less water enters the sewerage network. During heavy rainfall water enters the sewerage network from roofs/ driveways. The sewerage network can't cope with this water and sewage overflows into rivers and streams through emergency overflows. This sewage kills most life in the river and the resultant toilet paper/ rags isn't nice to look at.

Below is a photograph that shows what happens when a sewerage system is overloaded. The material you see will be a mixture of toilet paper, sanitary rags etc. If rainwater harvesting helps stop this pollution I think it is a good thing

When I flush my toilet I release x litres of water into the foul sewer; that happens regardless of my toilet cistern being filled with rainwater or mains water.

So at times of heavy rainfall when the sewers are having difficulty coping, how does it help having my x litres of rainwater entering the foul sewer instead of x litres of mains water?

I am not sure that you are correct in stating that the majority of houses in UK have a combined sewer, however that makes no difference to this discussion.

We all agree that during storms that sufficient rainwater enters the sewerage system to cause problems - that happens regardless of 10% of houses having combined sewers or 90%.

You haven't given any explanation why depositing x litres of rainwater in the foul sewer from a toilet, rather than x litres of mains water will improve the situation.

darkpool

because during rainfall the rain enters the storage tank instead of going into the sewer. i can't make it much simpler than that.

zeupater

darkpool wrote: »

zeupater, yes i agree from the sounds of it rainwater harvesting wouldn't make much difference/ any difference to flooding from sewers for your house.

But there will be houses/ businesses where rainwater harvesting will make a significant difference to overflowing sewers and raw sewage being discharged into streams.

For instance how about a football stadium? It's got a very large roof and a high demand for water to irrigate the grass and flush toilets.

regarding the cost of rainwater harvesting, it sounds like you were looking at a 'Rolls Royce' scheme. at it's most basic rainwater harvesting is a £20 water butt from B and Q.

cardew, the majority of houses in the UK have a combined sewer. so using rainwater to flush toilets etc will reduce water going into the sewerage system. this is because you are reducing the amount of mains water you are flushing down the toilet. i'm not saying rainwater harvesting will stop sewer flooding but it will certainly help.

Hi

I am in total agreement, rainwater harvesting will definately help to smooth discharge to the drainage system in normal conditions, but the point I am trying to convey is that it will not make much difference in storm conditions which are the primary cause of foul drain overflow. As stated previously, in my case 1/3" of rainfall would top up a half full 3500litre system, whilst in typical flood events you could expect something like a month worth of rainfall in a couple of days, so in my case this scenario would capture less than 2 tonnes of water and then dump a further 15 tonnes down the drain along with another 15 tonnes surface water from my drive thus reducing the stormwater drainage from my property by just over 6%. This percentage could probably be scaled to a smaller house with a smaller storage capacity system and remain typical.

The cost of the rainwater harvesting system I looked at was based on a simple filtered & pumped underground storage setup to feed a standard header tank, along with the controls to switch the pump on/off and provide mains water backup when necessary ... not rocket science & definately not a RR solution, just what is required.

The water butt solution is good for the garden & the pocket, I use them, however, when it rains hard mine literally fill from empty in a minute or two .... not much use for seriously reducing flooding.

Regarding buildings such as supermarkets, factories & football grounds .... many of these already have SuDS to reduce their immediate impact on drainage, allowing a more controlled release into the environment. A large manufacturing plant I was involved in the specification of in the mid-90's had massive storage under the car park even then, as has our local supermarket & many others. These systems intercept 100s or 1000s of tonnes of water in storm conditions and release in a controlled manner so as to help avoid flooding. As they are specifically designed for flood control they are naturally empty in order to maximise performance when it rains, unlike household harvested rainwater systems which are designed to operate as full as possible as standard.

Z

Rodders57

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

zeupater

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

Hi Rodders57

I dont know whether the referenced post relates to my posting, I'll answer as though it does.

Of course a housing estate will have an effect on the surface water drainage collection & of course, if you read my posts I agree in principle with household rainwater harvesting. My only concern is that people could be persuaded that domestic rainwater harvesting could be a major solution to foul water drainage flooding in sustained rainfall or storm conditions.

The figures I have supplied as examples are based on my property. I have allowed for a storage capacity which is three times the size of what has been quoted by installers for a retro-fit system, and have been generous to say that the system would be half full when a storm condition occurs. Of course, if anyone would like to dispute my figures as supplied they can and I will be open to correction if they are substantially incorrect, but I have backed up my position with logic and data, that's all I can do and it would be the task of anyone who disagrees to show that either the logic or the data is in error as opposed to the political correctness.

Z

darkpool

I don't think your 6% reduction is that typical. A typical house in the UK is likely to be about 60m2 plus 60m2 of driveway/ patio. if four people stay in the house i think it fair to say they use 150litres a day for the toilet/ laundry/ garden. over a year that's 54m3 of water. if rainfall is 1m a year that means a nearly 50% reduction in stormwater going into sewers. I'd imagine pubs etc could use all their roofwater for toilet flushing.

i don't think it necessary to bury a rainwater tank. i'd leave it above ground - that means no need to dig a hole and if you're clever you wouldn't need a pump for the water. that would mean a big cost saving.

i've designed a lot of SuDS features. I've never seen a supermarket/ football ground with any SuDS feature. I doubt if more than 1% of commercial buildings in the UK have any SuDS feature at all.

zeupater

darkpool wrote: »

I don't think your 6% reduction is that typical. A typical house in the UK is likely to be about 60m2 plus 60m2 of driveway/ patio. if four people stay in the house i think it fair to say they use 150litres a day for the toilet/ laundry/ garden. over a year that's 54m3 of water. if rainfall is 1m a year that means a nearly 50% reduction in stormwater going into sewers. I'd imagine pubs etc could use all their roofwater for toilet flushing.

i don't think it necessary to bury a rainwater tank. i'd leave it above ground - that means no need to dig a hole and if you're clever you wouldn't need a pump for the water. that would mean a big cost saving.

i've designed a lot of SuDS features. I've never seen a supermarket/ football ground with any SuDS feature. I doubt if more than 1% of commercial buildings in the UK have any SuDS feature at all.

Hi

I think that the problem with the calculations above are the relevance to high rainfall/storm conditions which lead to foul water flooding.

Lets consider the 60sqm roof you propose is typical and allow for a typically half full above ground (to save cost) 1000litre storage, as opposed to a smaller (lighter) unpumped loft tank, also assuming that the surface water drainage from the property is also 60sqm.

The rainfall requirement to collect 500litres of water to top up the tank is still 1/3" (8mm) .... a typical month would still have 83mm (1m/12) of rainfall .... the storm/heavy rainfall event would still deliver a month of rain in a couple of days. The result would be 500litres collected, the roof would dump 4500 litres to drainage and the rest of the property would need to drain a further 5000 litres. In this scenario there would be a 5% (500/10000) reduction in the stormwater immediately released to drainage ... which is in line with the 6% from my property, thus reinforcing the position that domestic rainwater harvesting to reduce foul water flooding in storm conditions is unlikely to have much of a beneficial effect.

HTH
Z


Note: It is wise to note that storage of rainwater in a tank above ground level will expose the contents to higher temperatures and light conditions encouraging bacteria and algae in untreated water, anyone wih a water-butt will testify to the effect of this in summer.