Water saver for shower.

Some time ago, maybe a few years, there was a series of posts about saving water when running hot water for a shower. Someone had made up a system whereby hot water would divert back into the fresh water tank until it got hot than you could open the faucet and get hot water right away. Part of the system had a piece of tubing that would change color when the hot water went thru it alerting you to the fact the shower was ready.
Any chance someone remembers this and can suggest who made the kit? Any info would be helpful.
Thanks.