The a shower design by a company called orbital systems that uses nano-tech filters and smart sensors to save 90% of the water that's used while showering by reusing water.

They have tested their product with commercial customers and are taking preorders for direct to consumer sales. If the water prices are high the shower pays for itself in a few years.

It would make sense to do the same thing with sinks. Reuse the water by having good water filtering. Having a sink that can recycle it's water also allows the sink to clean dishes that you put into the sink. It just needs sensors, a camera and a few motors to be able to redirect the faucet.

Once you filter most water at the tap it's also much easier to use rainwater.

Toilets should have sensors to make smart decisions about how much water is needed at a particular instance and use exactly as much water.

Silicon Valley should build tech to reduce domestic water usage and make bathrooms and kitchens better.

Most water usage isn't due to domestic usage but farming. Farmers will have to do with less water or go out of business. Maybe the can also drastically improve by going high tech. Israel seems to have figured out how to do agriculture with less water, maybe Californian farmers can learn from it.

Given California's issue with high housing prices, it might make sense to allow anybody to build housing in land that's currently zoned for agriculture.