The Water Balance

A water balance accounts for everything entering and leaving the site. Most organisations discover a substantial unexplained gap the first time they build one, and the gap is usually leakage.

Inputs

Mains supply, abstraction from borehole or surface water, harvested rainwater, recycled process water, and water contained in delivered materials.

Outputs

Trade effluent to sewer, surface water discharge, evaporation from cooling and drying, water in product, water in waste, irrigation, and losses to leakage.

Building one

• Start from the incoming meter reading over a period, and sub-meter the largest users.
• Measure or estimate each output, including evaporative losses from cooling towers, which are frequently the largest single consumption on a site and are invisible without calculation.
• Compare inputs against outputs; the difference is unaccounted water.
• Read the meter at a time of no production — overnight or over a shutdown. Any flow at all is leakage, and a continuous small flow amounts to a large annual volume.

Where reduction usually is

Leaks, continuously running taps and hoses, once-through cooling, over-specified wash-down, cleaning by hosing rather than sweeping, and cooling tower blowdown set more conservatively than necessary. Reduction is usually a matter of a dozen small fixes rather than one project.