Not much. About 2 glasses of water (500ml) per average wash. You use 4 times this amount (2 litres ) when you wash your hands.
Did you know that a 10 minute shower can use as much as 120 litres? So the amount of water you would use with our bidets over a whole year could be less than having 2 ten minute showers.
A lot of water is used in the manufacturing processes required to produce the toilet paper and a lot of chemicals and dioxins are used in this process. If you don’t use toilet paper, apart from saving money every week, you will also be doing your part in reducing the pollution discharged into streams and rivers, generated by the manufacture of toilet paper.