Water related technologies
There is sufficient rain water delivered to our homes in the UK, for us to be self-sufficient on this resource.
Bore holes are quite expensive, but they do provide vast amounts of water which could easily be shared between several properties.
Water saving technologies
Water saving shower heads
These devices are cheap and if you find the right one, they are also very effective.
Almost a third of all the water we consume is used to flush the toilet. A composting toilet would remove this consumption.