Evaporation
Evaporation is the loss of water from a pool's surface as water molecules escape into the air, which concentrates dissolved chemicals and raises TDS.
Definition
Evaporation is the loss of water from a pool's surface as water molecules escape into the air, which concentrates dissolved chemicals and raises TDS.
Typical Values: Evaporation rate: 0.5–2 inches per week depending on temperature, humidity, and wind
In Plain Language
Pool evaporation is significant in hot, dry, or windy climates. Evaporation removes pure water but leaves dissolved minerals behind, increasing the concentration of calcium hardness, CYA, TDS, and all other dissolved compounds. A pool in a hot climate can lose 1–2 inches of water per week to evaporation. Refilling maintains volume but does not reduce elevated dissolved mineral concentrations.
Why It Matters
Evaporation explains why pool hardness and TDS increase over a summer season even without adding hardness-related chemicals.
Typical Values
Evaporation rate: 0.5–2 inches per week depending on temperature, humidity, and wind
Last reviewed: 2026-06-01