Here's the latest concept I've been pursuing. This week I'm trying to source the solenoid valves that will select city or rain water. The boss tells me that geothermal systems use electrically actuated valves like this, so I'm off to learn about that.
I tried using a
simple venturi pump to suck water out of the reservoir and mix in with the city water, but the toilet requires such a low flow, that it just didn't work. So we'll have to use a pump.