The EcoDrain™ is a unique patent-pending heat exchanger which transfers heat from hot shower waste water to cold incoming water. This cuts water heater use by 25%-40%.
This is for showers only. The hot shower water that goes down the drain is used to heat incoming cold water for the shower, thus saving hot water usage.
They say it hooks up easily. Perhaps for a first floor shower where you have a basement under it, but it would be difficult to retrofit in, say, an apartment building. Still, this is a great idea. The more ways we have to save energy, the better.