There are two ways in which we can classify our water use. One type is in-stream use; this includes hydroelectric power, boating and swimming, for example. While in-stream activities do not use up the water, they can degrade the water quality through pollution. The other type of water use is the withdrawal of water, and this classification includes household use, industry use, irrigation, livestock watering and thermal and nuclear power. Most withdrawals are consumptions, meaning that the activity uses the water and does not return it to the source.
The amount of water that is taken (or withdrawn) from the source is called the water intake, and the amount that is returned is called the water discharge. The difference between the water intake and the water discharge is the amount consumed.
Water intake – Water discharge = Consumption
The total amount of water that is used is called the gross water use. The difference between the gross water use and the water intake is equal to the amount of water that is recirculated. The recirculated amount is expressed as a recycling rate and is a good indicator of water efficiency.
Gross water use – Water intake = Amount recirculated (or recycling rate)