Does grey water system make sense for reirement home

I was reading on your website about recycling the hot water you use in the shower & sink. It showed a copper coil piece that gets installed in the plumbing. The hot water is routed to the storage tank to save on electricity in heating it for the next use.

My question, though, is since tankless water heaters heat the water on demand and are supposed to eliminate that storage process, does it make any sense to spend the money to recycle the hot water? Or would a grey water system - that uses the excess water from showers and sinks in the garden or elsewhere - be the beneficial system?

This is for new construction, a 2nd home near the beach that will eventually be a retirement home that we are trying to make as energy efficient/independent and as "green" as we can afford. Thanks!