What water shortage? How to harvest rainwater.

June 11, 2006

We’ve been looking into rainwater harvesting. With all this talk of water shortages and hose pipe bans and Thames Water’s recent request for drought status it seems more and more necessary. What is it? Storing rainwater from the roofs and using it to flush the toilets and potentially to do the washing too.
How big a tank?
How much water do you use?
Roughly daily use:
12 WC flushes per person @ 6ltrs per flush = 72ltrs,
plus, depending on how often you do your washing 1 washing cycle = 60ltrs
Calculating how much rain you can get each year obviously depends on the size of the roof. We’ve discovered that our neighbour’s roof drains onto ours so we have the benefit of that too. The tank we are looking at is approx 1.25m diameter by 1.5m high/long = 1500ltrs. That would serve a 4 person house.
Where to store it?
Either you store it high up the building and use gravity to feed toilets below or you put the tank lower down (in the ground) and pump it up to a header tank. Obviously pumping the water up to a tank takes energy and costs more but because of height restrictions and a 3rd floor bathroom, that’s what we’ve had to do. This will use approx 30 kw hours per year of electricity.
How much does it cost?
I’m still waiting for my quote. I’ll post it when I get it.
Here are some useful links:

rainwater harvesting