# Makeup Water — Utility Construction Glossary

Water supplied to a cooling system to replace what is lost to evaporation, drift, and blowdown. On evaporatively cooled facilities it is delivered through a dedicated main sized independently of domestic demand.

## Frequently asked questions

### Why does a cooling system need a dedicated makeup water line?

Evaporative cooling continuously loses water to the atmosphere, and the volume dwarfs domestic use. A facility on cooling towers may consume on the order of one to three million gallons a day per 100 MW of load, so the makeup line is often a large-diameter main with its own meter vault and backflow assembly rather than a branch off the domestic service.

### What is cooling tower blowdown?

As water evaporates, dissolved solids concentrate in the remaining loop water. Blowdown is the deliberate discharge of some of that concentrated water so solids stay within limits. It typically discharges to sanitary sewer under an industrial pretreatment permit, and many municipalities cap total dissolved solids, so the discharge line and any treatment are part of the site utility scope.


## Related terms

- [water-main](https://www.dunninfrastructuregroup.com/glossary/water-main)
- [backflow-preventer](https://www.dunninfrastructuregroup.com/glossary/backflow-preventer)
- [yard-piping](https://www.dunninfrastructuregroup.com/glossary/yard-piping)
- [flow-monitoring](https://www.dunninfrastructuregroup.com/glossary/flow-monitoring)

Makeup water is the defining wet utility scope on an evaporatively cooled facility, and its absence is the defining feature of a closed-loop one.

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Source: https://www.dunninfrastructuregroup.com/glossary/makeup-water
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