Short answer
Water does evaporate at night. A temperature difference between the water surface and cooler air drives moisture into the atmosphere, and wind can speed the process.
Key points
- Nighttime evaporation occurs when water is warmer than the air.
- Cool, dry nights increase evaporation rates.
- Wind pulls vapor away, raising loss.
- Covering a pool can cut evaporation by up to 90%.
- Heated pools lose more water after dark.
Water still evaporates after sunset. A warm surface and cooler, drier air create a pressure difference that pulls moisture into the atmosphere, and breeze can accelerate the loss.
Factors that boost nighttime evaporation
When the pool stays hot while the air drops, the temperature gap becomes a strong driver for evaporation. Wind, even a light breeze, moves the vapor away, preventing re‑condensation on the surface.
Reducing the loss
Placing a cover over a pool traps heat and keeps humidity close to the water, cutting evaporation dramatically. This keeps water levels steadier and saves on heating costs.
Frequently asked questions
Does humidity affect nighttime evaporation?
Higher humidity slows evaporation because the air is already saturated with moisture, making it harder for more vapor to enter the atmosphere.
Can a pool leak be mistaken for evaporation?
Consistent, gradual water loss after hot days and cool nights is usually due to evaporation, not a leak. A sudden drop or uneven loss points more likely to a leak.
Is evaporation still significant in winter?
Even in winter, if the pool is heated and the night air is cold and dry, evaporation can occur, though rates are generally lower than in warmer seasons.
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