Having created the water balance, you need to quantify and measure each element. Put all major water uses and effluent (liquid waste) sources in order and, starting with the largest, work out quantity and frequency of use.
There are various ways of measuring water use:
- water meters
- flow meters
- calculations from manufacturers' brochures or handbooks
- estimates based on your knowledge of the process
- timing how long it takes to fill a container of a known volume
To measure effluent, you can use similar methods, although in some cases - eg washrooms or rinse processes - effluent flow may often be the same as water use. If waste is collected by an outside contractor, they should be able to provide data.
You should allow for partial filling or overflows when assessing both water use and effluent disposal.
Recording the information
It's very important to keep accurate records on a water use chart or on a worksheet spreadsheet.
Recording quantities and costs data on a worksheet will help you to identify where you can save water and cut costs - see how to use your water monitoring information to save money.
Finishing the water balance
With all the information you now have you can complete your water balance. You may find it easier to split up the block diagram into different processes. The water balance should show:
- all known inflow points
- all known outflow points - whether as wastewater, liquid waste, product or evaporation
- amounts of these flows
In theory, the amount going in should be the same as that leaving, although this is rarely the case. You should, however, aim for an initial accuracy of plus or minus 10 per cent of the total water quantity you can account for.
It's also important to look for inconsistencies because these may indicate leaks, unauthorised, excessive or unnecessary uses or simply something that you have counted twice or missed altogether. Make sure meters are checked regularly and properly maintained, and that staff know how to use them.