100 Galen
If the toilet works each time on one flush, they use roughly half the water of a standard toilet. You would then use half as much a month on the toilet. They do not always flush completely on the first flush and the toilet is only a part of the water bill.
5 billion gallons per year
3 liters
You use anywhere from 1 cup of water to 5 cups of water to flush the toilet. This is per time you flush the toilet.
In a modern toilet you use 13 litres per flush.
It takes 1 bucket of water when we flush.
If it's a normal household toilet you simply lower the water level in the tank that's over and behind the toilet by adjusting the fill valve. There are many different designs so I can't tell you how on your particular toilet. Some ae as easy as turning a plastic screw and some are a real pita. If you adjust it and raise the water level too much water may run over into the overflow tube and it will just keep running. If you lower it too much your toilet may not flush completely. Generally I adust mine as high as they will go without overflowing in order to get a stronger flush. I have never needed or wanted to turn down a flush.
I believe it's 3 gallons
5 gallons
1.6 GPF.
There is about four to five gallons wasted if you flush a toilet but I don't believe that it makes a difference if the handle is loose or not. Unless, the toilet is leaking from the handle or somewhere else.
5 gallons