Flush loo with rain water


Postby NigelG » Tue Nov 04, 2008 9:37 am

Hi,
We are attempting to flush our loo with rainwater - with mains water as back up. We are not doing this because we have to but more because we would like to do our bit for recycling. We live in a bungalow and the rainwater tank (garden water butt raised on a stand) plus the loo are both at ground level. Up to now I have connected the tank directly to the loo via an underground pipe that was already laid in but the water pressure being generated by the height/weight of the water in the (190 litre) tank is only sufficient to push the water up to the underside of the cistern but for some reason not enough to push the water into the cistern. I guess the extra height or maybe an internal seal is preventing it until the incoming pressure is increased to over come it? Installing a header tank either in the loft or outside above the tank will be difficult and, for the loft option costly, so my thought is to install an inline pump (12v preferably) which automatically switches on and off when the loo is flushed. If it helps - the height difference between the bottom of the water tank and the top of the loo cistern is no more than 2 feet 6 inches but from the underside of the tank the pipe does drop down underground before going up into the property so from the lowest point (underground) to the top of the cistern is probably 4- 5 feet. My questions are:
1. Does the inline pump idea sound good to you and if so do you think I should place it close to the tank so to give maximum push effect or close to the cistern to give draw effect.
2. Is there a pump that automatically switches on/off when required?
3. Do you have a better idea!
4. Can anyone explain how atmospheric pressure works or basically why isn't the water weight/height in the butt enough to push the water up into the (much smaller) cistern! My understanding on this subject is lacking!
Thank you for your help
cheers
Nigel & Katie
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Postby plumbbob » Tue Nov 04, 2008 6:34 pm

Firstly, lets get the legal bit out the way which you probably already know about and I'm wasting my time, but anyway... You must be very careful not to allow any grey (rainwater etc not treated) water to enter the drinking water system. Obviously, there is a health hazard to you, but if any of this water was to syphon back into the water main, you would be in serious trouble. Installation regulations go to great pains to ensure that backflow contamination cannot occur, and you must ensure these regulations are adhered to.

You possibly have two options. Firstly, plastic ball valves are supplied with a choice of fittings for low or high pressure. Low pressure water will not force a valve set for high pressure open hence your problem. Sometimes the spare conversion part is clipped to the arm and looks like a little plastic funnel and is usually red or blue.

The second option is to buy a 12 volt pump as used in a caravan or boat. The system is normally under pressure and when a tap or valve opens and the pressure drops, the pump senses this and fires up.
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Postby Dave From Leeds » Tue Nov 04, 2008 8:55 pm

The important factor here as to whether your rainwater tank will fill your toilet cistern is that the level of water in the tank needs to be higher than the level in the cistern when full. If it isn't you will need a pump in order to fill the cistern from the tank. If there's not much difference in height between the level of water in your tank and the cistern water level when full, it will take a long time to fill up the cistern. Another option to a pump might be to simply raise the garden water butt further off the ground so that there is a substantial difference in level between that and your cistern.

With regard to a pump that turns on when the loo is flushed, it should be possible to purchase a simple level switch that could be wired into the supply to the pump so that when the water level in the cistern drops on flushing the pump will start and keep running until the level in the cistern reaches the level switch when full.

Are you taking the water into your toilet cistern through the same ball valve as your mains water or through a different one. I think you'll need some sort of shut-off valve otherwise, if the level in your rainwater tank is higher than your toilet overflow, water will simply transfer from the tank into the cistern then down the oveflow pipe. If you do go for the pump and level switch option you'll need to ensure that the level switch operates just below the level at which the ball valve shuts or the pump will not stop.

Looks like an exciting project to me. Good luck.
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Postby chris_on_tour2002 » Tue Nov 04, 2008 10:12 pm

i think a pump is a good idea and probably your only option - other than raising the water butt.

with regard to the underground pipe, the water level will rise up the pipe only as far as the point where it reaches a point of equilibrium that is to say when atmospheric pressure (literally the weight of the atmosphere when subjected to earth's gravity) of the water being pushed up the pipe = force of the water in the butt. normally you would expect the water to rise only to the level of the top of the tank max. but you also have the valve in the cistern to further increase resistance. i am not surprised that it does not work in its current configuration.

you could try using a low pressure diaphragm in the filler valve of the toilet - may currently have a high pressure. worth changing it over for the cost of a few pennies, if it works then happy days. may also be a high pressure flow restrictor in the filler pipe - remove if present.

from your post it seems that you already have a pretty good take on it and you are thinking along the right lines.
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Postby chris_on_tour2002 » Tue Nov 04, 2008 10:17 pm

further thoughts.. you may only need to raise your butt up so the bottom of the butt is higher than the top of the cistern.

and don't forget that the water level in the butt is variable - during dry spells the level of water will of course drop, consequently the pressure will also drop so your dual system is sensible... though not quite sure how it will work unless you install a mains-fed float valve in the rainwater butt. which may defeat the object somewhat?
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Postby NigelG » Wed Nov 05, 2008 11:51 am

Just a note to say many many thanks to all of you who have taken the time to reply. It’s the first time I have visited/used this type of forum and it’s really quite amazing!.. Similarly, as part of my quest, last night I was searching the net for a sensor/switch to control a pump and ended up sending an enquiry to a company in the USA from which I received a reply today pointing me to their distributor here which turns out to be close enough we have the same area code! small world hey.

I have to re-read all your suggestions yet and get my head round them but just to cover one item from plumbbob - yep I am very conscious of the backflow issue and have put in a (double) one way valve unit into the fresh water feed. Secondly I have also put in two independent shut off valves one for the rainwater and one for the fresh. and finally we are blessed with 6+bar of water pressure in our village! yep I kid you not in fact stiff enough that it blew a plumbers pressure gauge once, before I installed a pressure control valve in the new mains I installed... my point being that I don't think my water butt is going to challenge Anglia Water!

Plumbbob - on the valve idea which, if I can get that right, sounds the easiest way to go- our cistern isn't fitted with a ball cock valve but with a unit which is a vertical column in shape has a float unit at the top and the water seems to enter below residual water level which keeps filling very quiet. The discharge unit is separate from this and is controlled by a button in the cistern lid.. sorry for such a dumb description! Do you think there are low and high pressure seals for this type? and if so and I fit a low pressure one any ideas what will happen when I switch to my mains feed?

Many thanks again
Nigel
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Postby plumbbob » Wed Nov 05, 2008 9:09 pm

You will very probably be unlucky in finding a Torbeck (column) valve that works with such low pressure. I do notice however, Screwfix do one which works from 1.5 to 200 psi but then your water butt pressure is likely to be less than this. ( I think 1.5 psi is just over 1 metre of head, but don't quote me on this)

Some years ago, it was law that toilet cisterns were filled from stored water, hence the low pressure ball valve. Now this is no longer required valves are are rarely designed to work at such low pressure. Saying that, often, these new valves have flow reducers fitted in the column part of the valve. Some also have a filter. If you uncouple the feed pipe underneath the cistern, using a mirror or something, see if there is a plastic spiral type thingy about 2" long fitted up the pipe.

I you manage to get the cistern to fill at low pressure, if you switch over to mains even at less than the whopping 6 bar, at the very least, you will get wet, water sprays all over the place (I've seen it squirt out between cistern and lid) and worse, it may not switch off when full and the overflow won't cope.

Far better to couple to the butt permanently and find a way of keeping sufficient water in it - a hosepipe say.
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Postby NigelG » Thu Nov 06, 2008 7:58 pm

Plumbob, your 'spiral type thingy' beat my column description hands down! Thanks again for your ideas. I have made progress and things are looking good. I decided to try your idea of the 12v pump via a whale submersible borrowed out of our camper and hooked it to the end of the feed pipe from the butt and hey presto the cistern filled no problem. with this option I don't now have the worry of what happens when I go to mains if I modifyed the valve so happy days. next i went to the distributor and came away with 2 pressure switches FOC because they were interested in what I was doing. So tomorrow its wiring time and with a bit of luck I will have an automated rain water flushing loo by the weekend! many thanks again
cheers
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Postby NigelG » Sat Nov 08, 2008 10:31 am

I am now very close to having our system working i.e. I now have the submersible pump (whale 881) in the butt and on its own it is filling the cistern no problem. Next I have piped in a T to take the pressure switch. I have been given 2 to try; both are adjustable: 0.11 - 0.4psi and 1.0 - 4.0psi respectively and both have Common, NC (‘normally closed’) & NO (‘normally open’) terminals. In both cases I am getting the same result: if I use the Common/NC option the switch clicks on and off repeatidly making the pump works but it hunts/pulses and is very slow no matter how I adjust the pressure range but, it does stop when the cistern fills and starts again on demand. If I use the Common/NO option the switch is silent and the pump runs very smoothly and fast but once the cistern fills and the valve closes, the pump carries on pumping no matter what setting I try on the pressure adjustment. My guess is that the Common/NO option is the correct wiring option but neither switch is the right one (PSI range) to suite the whale pump I have.

By the way I did consider using a level switch to control the on/off function but, unless there is a wireless version, to wire in the switch (based in the cistern) back to the pump would be difficult to put in place so hence the pressure switch idea.

Does anyone know how the pressure switch works i.e. from the point of which of the NO or NC options is the right one to use and why?

Thanks again
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Postby plumbbob » Sat Nov 08, 2008 1:14 pm

Thinking about it now, I can see why the pressure switch option may not work reliably.

I should have thought the N/O option would be correct because using the N/C would reverse the operation, ie, switch the pump off when the pressure was low instead of on, so basically it wouldn't work.

If we assume the switch is working and wired correctly, maybe the problem is with loss of pressure in the pipework. Are you sure the pump is not allowing a backflow causing it to pulse? What about the cistern valve? Often these valves don't simply cut off the flow but continue to dribble for a while. Pull the float up with a finger. Does this stop the pump?
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Postby nitro23456 » Sun Nov 09, 2008 5:42 pm

Is this really worthwhile? I dont know how much it rains out your way, but Id be lucky for more than one flushs worth of rain every week!

Is it worth the money for the system in terms of water saved?.... or environmentally surely the plastics and substances involved in the parts outweighs the water saved?
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Postby Skids » Sun Nov 09, 2008 10:27 pm

Hi NigelG,

Google reuk.co.uk

you may get some ideas, great site

all thge best

Regards

Skids
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Postby BlueNose1812 » Sun Nov 09, 2008 10:54 pm

[quote="nitro23456"]Is this really worthwhile? I dont know how much it rains out your way, but Id be lucky for more than one flushs worth of rain every week!

Is it worth the money for the system in terms of water saved?.... or environmentally surely the plastics and substances involved in the parts outweighs the water saved?[/quote]

And the electricity used to drive a pump wastes more natural resources than are being saved.

The true environmental cost of all human activity is its monetary cost since all expenditure can be traced through to eventual energy consumption somewhere in the chain.
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Postby Greenman » Fri Nov 14, 2008 12:32 pm

[quote]Is this really worthwhile?[/quote]

I'm with you on this, though I understand what it is like saying this to an addicted DIYer. The answer is yes - because its there!

Having said that, I think I would just have a large vat somewhere open to the rain and also accessible enough to be out there to collect grey water from the washing machine by hand bucket.

Then, when you want to flush the loo with your grey water, just go out and scoop yourself a bucket toi throw down the pan.

You have yourself some daily exercise, you haven't used anymore virgin plastics or resources and you are doing your bit for water conservation. and yes - in Cornwall at least, it rains enough to justify collecting water to flush with as the garden very seldom needs watering.
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Postby plumbbob » Tue Dec 02, 2008 11:38 pm

Someone else asked me this today, so sat down and did a quick calculation about how cost effective this would be.

If we assume 4 people in a house flush the loo 3 times each (12 flushes) and each flush is standard 6 litres. That equals 72 litres/day. A standard water butt holds about 210 litres. That is only 3 days of supply!

Looking at the water bill, water is with VAT and everything, about £1.80 per cubic metre (1000 litres). So one water butt is worth about 38p.
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