[Orbiting_Rosie's_Head]

The largest water uses in a home are toilet flushing and clothes washing. I can't understand why homes are not built with a 10-20 gallon water storage tank with overflow valve in the attic. The water pump in a washing machine could be used to pump water from the washer to the storage tank, where it is then piped back down to fill the flush toilets, so that the wash water is used twice. Combine this with a toilet that has a divided two-flush tank, 1.5 gallons for #1 and 3-4 gallons for #2.

[The Red Zone]

This is called a greywater system. It doesn't work very well unless the greywater is disinfected (the germies clog up the tanks and valves but good).

[Sloth]

The water pump in a washing machine could be used to pump water from the washer to the storage tank, where it is then piped back down to fill the flush toilets, so that the wash water is used twice.

Good idea, but having seen the condition of washing mashine discharge pipes, I suspect that the dissolved detergents might deposit all over the toilet valves & supply pipes and cause problems.