Free, well nearly free. To flush the loo (half flushes 5L) 200 times (1m^3) costs about 276p on mains water. I.e. 124p to have the 1m^3 delivered up the pipe and another 152p to have it removed as sewage. Actually it's more 'cos I have not included the standing charges. To do the same thing on Rain water it costs about 15p worth of electric to pump it. It takes 1 min to fill the cystern and it is a 300W pump so 200 x 1min x 300W / 60min = 1kWh On mains electricity this currently costs me about 15p. If the sun is shining it is actually free but this is England and the sun don't shine a lot it cost 15p.

I used the Rain water to water my spuds etc all summer and found that the water level rarely went below 1500L from a total of 2200L. I.e. there was loads of reserve. So I could use some of this reserve for something else. Running a pipe to the downstairs loo was easy so I gave it a go. The pipe is in the insulation above the logs.

The big problem that occoured to me with using this water to flush the loo are that in winter the water in the tanks will go very cold and may freeze. I can live with that. The water in the pipes however is far more exposed and vulnerable to freezing than the tanks as the volume of water in the pipes is far less. The insulation (seen on the pipe above the logs) will help but it's not like getting water from the mains from 600mm below ground where the water is kept at 4-6C by the warmth of the ground.

The only solution was to use trace heater, after a surf I decided that was bloody expensive, so I'd best do my own version. I did some experimenting with the cables I had lying around and found I had 300m of Tri Rated 7/02 whose resistance is 0.1 ohm/m. If I wrapped this round the pipes (there and back)and pass 8 Amps through it and it would put 12W/m of heat into the pipes. As you can see the external pipe was plastic and to ensure the water got the heat quickly I put the wire inside the pipe. The rest was externally wrapped.

At first I fed the power to the wire from a transformer and controlled the temperature of the pipe with one on the generic controllers I had built. I found however that Toroidal transformers are particularly bad with in-rush currents these can be as much as 80 time full load current.. This one took out a 16A MCB regularly. The MCB has a fusing factor of 2.5 so thats 2.5 x 16 = 40A in-rush at least. I did buy some 5A 10ohm NTC thermistors to stop this but before they arrived I had another idea.

Next I used a Switch Mode PSU. The output is still isolated from the mains to 2KV and the voltage is adjustable and therefore the power is. And the chap that designed it took care of the in-rush problem too. This worked a treat... Again the wiring needs some work in this photo but this was the prototyping stage.

to allow myself to choose the source of the water and stay within the water regs I have two separate water feeds each can be isolated and neither are connected to each other. I have two compact float valves and the over flow is built into the new flush mechanism. I guess I could even turn both on.

I have now connected the upstairs toilet in the same way i.e. two separate supplies. I will take some photos soon (But they are very similar it's just the pipes are inside and under the bath). The biggest surprise is just how much water I actually flush down the loo. Since I have done this the water level has plummeted from around 1500L to 500L we have had three lots of rain about 2-3mm each giving about 200L each time but the level is still dropping quickly. Take a look at the graph... for reference I connected the upstairs loo on 2011-10-03.