[foreigner]

I used a toilet once that was connected directly to the sink next to it. The sink had a faucet but no controls. When you flushed the toilet the water started coming out of the faucet in the sink so you could wash your hands, and then was routed from the sink's drain directly to refill the toilet's tank for the next flush. When the tank was full the sink shut off automatically.

It was genius! So simple and cheap yet effective. An interesting side effect is that after you flush the toilet the sink's faucet runs for quite a long time, which really makes you appreciate how much water is going in to each flush. Why don't all toilets work that way?

[voisin]

This sounds amazing. Was it just a proof of concept or an actual marketed product installed somewhere? Commercial or residential setting?

[jaclaz]

Something along this approach has been used in "modern" house hydraulics in the last few years here in Italy, though not common, as it is used only AFAIK in self standing houses (not apartments buildings).

In practice there is a reservoir where the "almost clean" waste water (i.e. what comes out of the bath sink, bidet and shower/bath tub) is accumulated.

Toilets are fed by a pump with water coming from this reservoir, in practice you use the same water two times.

[hexa22]

It’s an actual product. My grandma in Australia has had one for 10 years.

I’m guessing it never took off because we don’t have that much of a water shortage in most places that washing hands is a luxury.

[foreigner]

It was at a place called Cypress Valley outside of Austin, TX. https://www.cypressvalley.com

Note this was many years ago...

[leipert]

Pretty common in Japan, if I recall correctly.

[cbmuser]

Yep, used these myself multiple times.