No, rainwater is not seawater. While rain often originates from evaporated seawater, the evaporation process leaves behind the salt and other impurities.
The Evaporation Process: Why Rain is Fresh
The sun's heat causes water from oceans and other bodies of water to evaporate. This evaporation process only involves the water molecules (H₂O), leaving behind dissolved salts and other heavier substances like minerals and sediments. The resulting water vapor is essentially pure water. When this vapor condenses and forms clouds, and subsequently falls as rain, it's freshwater, not seawater. Several sources confirm this process, including Let's Talk Science and the Chicago Tribune.
- Evaporation: Only water molecules evaporate, leaving salt behind.
- Condensation: Water vapor forms clouds, still free of salt.
- Precipitation: Rain falls as freshwater.
Exceptions and Clarifications
While generally true, it's important to note that rainwater isn't always perfectly pure. It can pick up pollutants from the atmosphere as it falls, such as dust, chemicals, or even slightly acidic components. Also, in rare circumstances, sea spray can be carried inland by strong winds and contribute slightly to salinity in rainfall near coastal areas. However, the overall salinity of rainwater is significantly lower than that of seawater. As noted in a Reddit discussion (r/explainlikeimfive), rainwater isn’t always safe to drink due to potential contamination.
In summary: Rainwater and seawater are distinct due to the purification process of evaporation. Rainwater is generally fresh water, while seawater is saline.
