Is Rain Water Salty?
No, rainwater is not salty. The process of evaporation, which forms clouds and eventually rain, leaves behind salts and other impurities.
When the sun heats the oceans, water evaporates. However, only the water molecules (H₂O) evaporate; salts and other dissolved solids remain in the ocean. This is a process of distillation, resulting in pure water vapor. This vapor forms clouds, which eventually release the water as precipitation – rain. Therefore, rain is essentially fresh water, even if it originates from the salty ocean. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
- Evaporation: Only water molecules transition to vapor, leaving salt behind.
- Condensation: Water vapor forms clouds.
- Precipitation: Water falls as rain, free from salt.
While rainwater is generally fresh, it can become slightly acidic due to the absorption of gases from the atmosphere, but it is essentially not salty. [4]
In contrast, the salinity of ocean water is a result of the accumulation of dissolved minerals over millions of years. Rivers continuously carry dissolved minerals into the ocean, and the evaporation process concentrates these minerals, increasing the ocean's salinity. [5]
The typical total dissolved solids (TDS) in rainwater is very low, usually 20 mg/L or less. [6] This contrasts sharply with ocean water, and even freshwater sources which contain varying levels of dissolved minerals. [6]
