Dilution
Dilution refers to the reduction in chemical concentration in pool water caused by adding water (rain, refill, splash-out).
In Plain Language
Dilution reduces all dissolved chemicals proportionally. A 10% dilution (replacing 10% of pool volume with fresh water) reduces all parameters by 10%. Dilution is the only way to reduce CYA, calcium hardness, TDS, and salt. Rain dilution is significant after heavy storms — a 1-inch rainstorm adds approximately 600 gallons of near-zero-chemistry water per 1,000 square feet of pool surface, which can significantly change TA and hardness in a small pool.
Why It Matters
Understanding dilution helps explain why parameters drop after heavy rainfall and why partial drains are the only way to reduce certain parameters.
Typical Values
Last reviewed: 2026-06-01