Simple, smart tech

This is a basic one, and yet pretty sweet. Someone has come up with a heat exchanger which transfers some of the waste heat from your shower water going down the drain to the cold water heading to the faucet. Incredibly simple really, but it cuts hot water use from showering by as much as 40% (seem s a little high to me, but even %10-20 would be sweet).

It really is not complicated and so should not be expensive. One of the few smart and actually economical 'green' ideas I have seen in a while.