How Clean is Rainwater?

Most people learn about the hydrologic cycle in elementary school. As adults, we probably remember the basics about evaporation, condensation and precipitation. The basics are that when water in oceans, creeks or lakes is heated, the liquid stage of water changes to the gaseous form and evaporates, rising into the atmosphere where it cools and forms clouds. This is the condensation portion of the hydrologic cycle. And just like a sponge, once enough water has condensed into a 'heavy' cloud, it can't hold any more water and the water, precipitation, will begin to drip out. Precipitation can be rain, snow, hail or sleet, depending on the temperature in the atmosphere and lower down near the ground.

That brings us to the topic of purity and pollution. It's a given that almost every sentient being on the planet knows that there is rampant pollution all over the globe. So, does this mean that all rainfall is polluted to some extent? The answer is no. We've all heard of acid rain, and this is a fact. However, even with acidic compounds trapped in the atmosphere, rainfall can still be as pure as it once was. This is because of the evaporation stage. When the sun heats up the water, whether it's in a puddle, pond or the ocean, the water undergoes the transformation from the liquid stage to the gas stage. As a gas, the two hydrogen and one oxygen (H2O) molecules are the only molecules bonded together, which simply put, means that pollutants on the ground or in the air, can't be picked up. As the gaseous water rises up into the atmosphere and condenses, it's in its purest form, made up only of the two hydrogens and one oxygen.

Now, as the condensed water gathers into clouds, it's still pure. But when the precipitation begins to fall, any pollution, or acid, will indeed be picked up in the water drops or carried on the snow flakes. Then as it hits the ground, the pollution will follow. It rain falls for any length of time, the pollutants can be cleaned from the air and the rain will again be relatively pure. If you want to collect rainfall for any reason, whether it's to wash your hair or put on your indoor plants, you can always test it with a litmus paper strip to determine its acidic content. Most of the time, waiting until the rain has been falling for a day will be good enough to cleanse the air. It can be collected then and will likely be free of most pollution. It's good to know that in this dirty, polluted world, there is still something on the planet that is pure and clean.