Rainwater Toilet Flush




Introduction: Rainwater Toilet Flush

For a few years now I have been thinking about using rainwater to flush our toilet. Finally, I have got round to it.

The motivation was not so much financial as ecological, it seems such a shame to use clean drinking water for flushing the loo when there is rainwater available.

This Instructable is more about the idea and what it entails than about dimensions and costs. Speaking of costs, it probably cost me more to put it all together than I will eventually save on water costs. As work progressed complications arose requiring modifications which cost more than I originally envisaged. You know what it´s like - "I´ll bung something together using stuff from around the workshop".

In the end I needed:

1 big water tank on a pallet

3 100 litre rainwater barrels

1 drill-operated pump (Wolfcraft - metal bodied)

1 12 Volt battery-operated drill (batteries were defunct, so was lying around in the workshop)

Quite a lot of concrete mix

A lot of hose - about 50 metres (depends on how far the tank is from the house)

Same amount of PVC piping for said hose

A few metres of Pex-Al-Pex tubing (and fittings) to connect the toilet to the outside piping

1 reed valve and float (from China)

Some wiring and spade connectors (from dead washing machine)

1 12 Volt automotive relay (the highest operating current you can find)

1 float valve (for gravity-fed feeding troughs)

1 Solar panel and battery (which I already had for emergency lighting)

And many other things which I may have forgotten or you will deem necessary ......

Each step includes photos and an explanation.

Step 1. The water system

Step 2. The electrics

Step 3. Pros and cons

Step 1: The Water System

The rainwater is collected in a large standard plastic water tank on a pallet. Rainwater comes from the roof of a small shed-cum-greenhouse at the top of the garden and is situated away from the house at about first floor level. Originally I envisaged a gravity fed flush system as the main toilet is on the ground floor. However, I came across several problems along the way which ruled this out. The first issue was that it took quite a while to refill the toilet cistern after flushing. The second problem was that a second float valve would take up too much space in the cistern - the original float valve remains in place so that both systems (rainwater and mains water) can be used either separately or together.

The first thing I wanted was to have the rainwater filtered through a primitive sand filter. There are not too many impurities in the rainwater tank, but I thought the toilet bowl could become discoloured with impurities, algae, etc. Also, there is the hygiene risk aspect of rainwater to consider. I know there are certain rules around the world for the use of rainwater alongside mains water in flushing systems. However, in my system there is no chance of rainwater entering the mains water system, and as for what is normally in the toilet cistern itself (rust, mineral deposits and a little bit of mould too), well that is probably worse than unfiltered rainwater.

So the rainwater from the main storage tank is fed slowly through a very basic sand filter into a storage system. The sand filter (in the photo, lurking behind the rainwater tank) consists of two 100 litre plastic barrels (one for the filter and one for storage) set in concrete for longetivity, with the filter barrel slightly higher than the other. The filtered water has to be topped up every few days - a disadvantage that could be solved with an automatic valve system (maybe next year ...). There is about 40 cms of gravel at the bottom of the first barrel with about the same depth of sand on top. Both layers are separated with a perforated plastic sheet. The filter is filled from the bottom and overflows into the next (storage) barrel. This is a quick filter (removes solid impurities but the water is NOT drinkable) and it takes about 45 minutes for about 100 litres of water to flow through.

The filtered water is then led, through a hose buried in the ground (encased in a PVC pipe), to another storage tank at first floor level on the house wall. There is not much logic in this extra tank, it is the result of my first idea of a gravity fed system. This reservoir can be seen in the photo, wrapped in aluminium moisture barrier to prevent algae from forming. From this tank the water fills a small reservoir (see step 2) at ground floor level. A 12V drill operated pump delivers the water from this storage reservoir to the toilet cistern.

There is a float and a reed valve in the toilet cistern which activates the pump, thus filling the cistern itself. The float and reed valve activating the rainwater system is extremely compact and simple, thus enabling me to leave the mains float valve in position. The advantages: In the case of a lack of rainwater, you can simply turn the mains water tap on and switch the electric pump off. You can also have both systems working at the same time if you haven´t much rainwater. This way the rainwater probably represents about one third of the flush. My loo cistern was equipped with holes for left and right hand mains water connection, so I simply plumbed the rainwater into the vacant hole, which is above the water level in the cistern so there are no issues with water leaks there. For the outside to inside connection I needed about 4 metres of pex-al-pex tubing - easy to connect, bend, etc.

In the image of the toilet cistern the rainwater connection is on the left side. The short hose just takes as much water away from the connections to the reed valve as possible. The wires and connections (12V) are all sealed with blobs of sealant. The wires from the reed valve go through the input rain water pipe itself to the pump outside the bathroom. The advantage: it looks neater, the disadvantage: I don´t know what problems could arise over time - disintegration of wire insulation, clogging up, etc..

Step 2: The Electrics

I didn´t really want any electronics at all. However, as I have already written, my idea of a gravity fed flush system just wasn´t practical so I came up with some sort of a compromise with a 12V, battery operated system and a solar charging setup.

The pump is actually a 12 volt drill-powered water pump activated by a reed valve in the toilet cistern and is connected to a car battery which is in turn charged by a solar panel. When you flush the toilet the rainwater float in the toilet cistern descends and the reed valve is activated. This sends a signal to the relay outside on the panel next to the drill. The relay connects the drill to battery and spins the pump. When the toilet cistern is full, the float rises, the reed valve is open, thus disconnecting the relay and the drill stops spinning the pump.

The pump body is bolted to a galvanised metal base plate bolted to the top of the outside reservoir. The drill, with the lower part where it would normally slot into the battery pack removed (with a hacksaw), has its chuck attached to the pump and is only clamped to the base plate with a U-bolt.

This setup is not exactly ideal and, for the future, I am considering using a submersible yacht pump. So far though, it is satisfactory - I will use the rainwater flushing through to maybe the beginning of November and then disconnect it until March, giving me 8-9 months of service. I live in the Czech Highlands and, even in today´s global warming world, we can still expect minus 20 centigrade during the winter, so it would not be feasible to use it over the winter. The solar panel copes perfectly with charging the battery even after repeat flushing.

Alongside the electrical layout in the photos you can also see the T-junction where the wires from the reed-valve exit and continue to the relay. There is also an on/off switch on the base plate near the pump body. The small reservoir tank with the float valve outside is necessary as the pump is not equipped with inlet and exit valves and thus the water would probably seep through the pump into the toilet cistern.

Step 3: Pros and Cons

Many of the pros and cons have been mentioned throughout the instructable so I´ll just add and recap:

On the plus side:

1. I´m really saving pure drinking water - I reckon on average about 150 litres over 4-5 days for 2 adults with adults and kids visiting on and off. It´s a wonderful feeling to be able to thumb your nose at the water board!

2. Although it´s pumped, it´s off-grid - water and electricity.

3. It´s a really reliable and efficient system - even though I say so myself. Sorry. It has only required a squirt of oil into the pump itself - that´s just because there´s a picture of a wee man doing just that in the instruction booklet ........

4. You can switch from rainwater to mains water in an instant.

5. You can combine rainwater and mains water - but probably not save very much.

And the minuses:

1. You have to check the rainwater level in the storage tanks every few days and top it up - task for next season.

2. It is probably unnecessarily complicated - a purely gravity-fed system would be ideal.

3. There´s a lot of hard work in it - in the photo you can see the general layout of the situation from the shed/greenhouse to the house, I´ve buried about 40 metres of hose (in a PVC pipe) across the garden, which required a lot of digging and filling in.

4. I´ve completely lost track of the costs, but am realistic that I´m not saving much in water costs now or in the near future. Water bills here in the Czech Republic are not as draconian as in the UK (even though we still complain), but will definitely rise in the next few years.

5. The system cannot be used during the winter due to heavy frosts. However, I still expect it to function for 8-9 months of the year.

6. Once or twice the reed valve stuck in the "on" position and needed a tap to switch it off. It hasn´t happened for a few weeks now, but maybe I should get a better quality one.

7. And yes, I could use water from closer to the house but those big tanks are a bit of an eysesore, and I haven´t got much space there.

Be the First to Share


    • Puzzles Speed Challenge

      Puzzles Speed Challenge
    • CNC Contest 2020

      CNC Contest 2020
    • Secret Compartment Challenge

      Secret Compartment Challenge

    7 Discussions


    1 year ago

    Hmm, I'm not sure if my idea works, this is for my dream house. I will have a bunch of tanks connected to one another to store the filtered rainwater, I will also have mains water connected to the storage tanks, a float will stop the mains water when the tank is 10% full, enough for every toilet in the house to have one flush at the same time, rainwater can fill up the remaining 90% via gravity, and overflow goes to garden.


    3 years ago

    I omitted: The more money I saved is because with rain water you don't have to use anti limestone product (where we live the water is very "hard"), and other type of chemical product to clean your toilets. I simply add some chlorine in the water tanks (to avoid algaes, bacterias, ...), and I use a very small amount of cleaning product to clean my toilets. Saved money: something like 2 euros a month.


    Reply 3 years ago

    Thanks for your remarks. You have been very scentific with calculating the costs of your system - good work! I´m too lazy to do that - but I probably should.

    I can´t use too much chlorine in my toilet because we have an aerobic treatment system. I´m hoping to use the waste water for watering the garden.

    The water costs here are much the same as here in the Czech Republic. Where are you?


    Reply 3 years ago

    Sorry for the late reply ... :/

    Here in France 1000 litres cost 3.3€. Each day we save 0.11€.

    A big saving occured last month: we had a huge storm and some trees felt down, cuting the pipe that brings water to our house. Thanks to this system we were able to use our toilets, and I could take the time to repair the pipes by myself during the next week end, instead to call a plumber plus loose a working day to follow its work.


    Reply 3 years ago

    Thanks for the information. It´s great when you are independent when there is a crisis. We were without electricity all evening last month after a storm and we used our emergency LED lighting off the solar system - the only house lit up in the neighbourhood.

    Our water is cheaper than yours - just over 1€ - but the incentive to save is still there. We have just switched to rainwater this weekend after the winter (we can´t use rainwater at - 20C in the winter!) so hope to get 9-10 months of free flushing.

    We only pay for water here in our village, but in towns people pay for water sewage treatment. This complicates the use of rainwater then - there must be a separate meter for measuring waste water from rainwater. If you have time, I´m curious how this works in your part of France.


    3 years ago

    Great instructables, thanks for sharing this !

    I made such a system 4 years ago: I
    already had 3600 liters tank to water my garden and solar panel and
    batteries for another usage, so I only considered the cost of bringing
    water to the toilets.

    First I measured the water used in the
    toilets: 2 adults and 2 (very young boys): 30 l. a day (here, 1m3 costs
    3.2 Euros): 35 euros per year ! To measure this I placed a flow sensor
    wired to an arduino/raspberry pi. Water cosumption is logged in a DB and
    graphed using some php scripts.

    The complete system: pressure diaphragm pump (12v), pvc tube, new toilet flush, water connectors: cost 89 Euros,
    so it was ok if the whole system work for more than 3 years. During the
    last winter, my pump froze ... I had to buy another one (15 euros)...
    And finally, last month I had my last 94th euro refunded ! Now water in
    the toilets are "free".