How much water goes down the toilet when you flush?

Generally, modern toilets are required to be low flow, which is 1.6 gallons (6L) per flush. Older toilets were 3 gpf (11L). Modern toilets vary in the amount of water required to flush them, from 6L to 3L. Some have a dual flush system allowing solids (faeces) to be flushed with a full volume flush, say of 6 or 4.5L, and liquids (urine) to be flushed with a smaller volume flush of about 3L.

It is not possible to flush properly a toilet with less water than that with which it was designed to be flushed. Low volume flush toilets have been designed to work efficiently with a smaller volume of water.