Geologist What Does Rain Do To Contamination

How can rainwater be contaminated?

Consider the raindrop falling through the air: any aerial pollution would be absorbed by the raindrop. Even over UK, Sahara dust has been carried north by hurricanes and ultimately deposited. Rainfall washes out such pollution and on occasions the rainfall will be muddy and make a right mess of your car.Rain also washes out traffic pollution: nitrogen oxides in a city causes a haze over the city-scape as viewed at a distance and vantage point. For example, from the top of Mount Vesuvio, look in the direction of Naples on a hot day. You will see the nitrogen oxide haze obliterating the city-scape, but after a rain shower the view of Naples is much clearer. The rainfall would have absorbed the pollution or otherwise removed the pollution from the atmosphere.Contamination also depends on how you collect rainwater: if you have roof water channeled and piped to water barrels, the rainwater will pick up material, which is on the roofing, like mosses and lichens and other mineral matter. This contamination could cause the water to be green, when in the water barrel.Even in pristine areas rainwater becomes a mild carbonic acid as it absorbs carbon dioxide from the atmosphere.

What is rain water and how can it be contaminated?

Rain water is the condensation of evaporated water, a continuation of the water cycle.  It can be contaminated by airborne pollutants like exhaust from factories and power plants which can carry sulfur compounds which turn into acid rain. This is probably the most famous example since it causes widespread problems.  Acid rain corrodes metal, drops the pH of the soil, and used to cause all kinds of problems before the EPA tightened restrictions in the US.  It may still be a problem in other countries.

Does rain water contain a salt?

In theory, rainwater is like distilled-water*, but it gets its compositions largely by dissolving particulate materials in the atmosphere especially the troposphere - when droplets of water nucleate on atmospheric particulates, and secondarily by dissolving gasses from the atmosphere.  In open ocean and coastal areas they have a salt content essentially like that of sea water (same ionic proportions but much more dilute) plus CO² as bicarbonate anion (acidic pH).  Furthermore, sea spray, carried aloft by winds blowing across the ocean, contributes to dissolved constituents in rainwater. Although dissolved minerals from spray are more abundant in coastal areas, they occur throughout the atmosphere. Sea spray is the primary source of chloride (Cl − ) in rainwater and a significant amount of sodium too (Na + ).(After the third or fourth heavy rain of the monsoon season, I collect rainwater for use in the batteries connected to the solar panels here at home. I may not be able to do it if I am in the city because of the air pollution)Needless to mention, terrestrial rainwater compositions vary geographically.  The compositions vary significantly from place to place because the regional geology can greatly affect the types of particulates that get added to the atmosphere. Likewise, sources of gaseous acids (SO³, NO²) and bases (NH³) vary as a function of biome factors and anthopogenic land use practices. Each of these gasses can be added in varying proportions from natural and non natural input sources (actually non-natural sources of SO³ and NO² far outweigh natural ones). Particulate load to the atmosphere can also be greatly affected by human activities.Rainwater is almost always slightly acidic because it interacts with carbon dioxide  (CO² ) in the atmosphere, forming Carbonic acid (H²CO³). Some of the carbonic acid in the rainwater then breaks down, producing more hydrogen ions and bicarbonate ions, both of which are dissolved in the rainwater. Finally, local climate - especially the amount of rain in one area compared with another - will also affect the solute concentrations in terrestrial rainwaters. The result is highly variable compositions, so there isn't one simple formula. Fresh Water, Natural Composition

What are the geologic formations that store water?

All rocks and rock formations can store some—repeat, some—water. The deepest rocks yet drilling into had water in them.But for practical water storage, you want a rock formation with a lot of porosity. Highly fractured granite sometimes makes a good aquifer. It has the advantage of usually being pretty clean, not having a lot of soluable minerals to contaminate the water.Fractured limestone does this too, and has the further advantage of neutralizing acids. Limestone layers very often have water channels within them, dissolved by the acidity of rain water. You can literally have underground rivers in limestone formations.Coarse sandstone beats all these, in both porosity and permeability. But a lot of formations are not true rock, rather, gravel and soil. Loose and unlithified (not yet turned into rock) sediments, especially those deposited into water by rivers, tend to have large spaces between particles which can both store water, and allow its passage. One of the keys is not having too much clay, which can seal up water channels.So can major faults. Most large faults are not just simple, thin cracks but zones of fractured rock which often carry a lot of water. Granted, faults also tend to carry a lot of minerals, many of which may be toxic.