I went to the local aquarium the other day. Among the fishes and corals they had a big tank with a toilet seat standing in the middle, big dull looking fishes swimming around it. A sign next to the tank said that the capacity of the tank was 30 000 litres, equal to the amout of water a two-person household uses every year flushing toilet. People are using fresh water to dispose human waste. That's a a lot, especially in this world of climate change and warming temperatures. Soon fresh water will be a scarcity - it already is in some areas.
A long time ago a solution was posted on Normal Room. The image showed a combined toilet/sink. The water used in washing hands went straight to the toilet's water container, and was then used to flush the toilet. Excellent - no problem flushing the turdies with dirty water! The photo was posted from Japan, so I assume that it's a japanese invention. That naturally doesn't surprise anyone, I believe. That kinda combination is also a great way to save precious space in bathrooms.
A toilet seat in Hiratsuka, Kanagawa, Japan