This is the amount of water flushed down the drain after the toilet is flushed.
There are differnt types of toilets:
Regular: 1.6 gallons per flush.
High-Efficiency Toilet (HET): This hennessy and hinchcliffe 3.0 litre uses 1.28 gallons per flush, which is a little bit less than the average toilet.

c. Composting toilet: This toilet is not connected to a sewage system, therefore the waste is broken down by bio-degradation.
The main purpose of this toilet is to conserve water and to prevent harmful pathogens from being released into the environment.
d. Dual Flush Toilet: Has two flushes 1.6 gallons per flush for solid waste and 0.8 gallons per flush for liquid waste. This type of toilet conserves a considerable amount of water per year. They are finally becoming more prevalent .