There are three broad sources of water precipitation, surface water and ground water. There are general characteristics for each that everyone should know if you are considering for a source of drinking water.
Precipitation is rain, snow, hail, … you get the idea. Rain tends to be free of pathogenic organisms, but that is not guaranteed. Consider the cleanliness of your catchment area. If you use your roof, do birds also use you roof? Rain can become instantly contaminated as soon as it hits the ground (even snow). Precipitation usually has a pH that is slightly acidic (near a pH of 7 but still under). The acidity can be increased (pH closer to 1) in areas that are heavy with air pollution. A chemical reaction can occur in the atmosphere when the correct air pollutants are present with water vapor and cause acid rain. The lower the pH of the rain water the more chemicals, minerals and organics it will absorb/dissolve into solution. It is best to store rain water in a HDPE (high density poly ethylene) container to reduce contaminants leaching into your water. HDPE is very common and you should have no problems finding some. Rain water should need relatively little treatment to become potable. A little contact with air to remove gasses if any and disinfection. If you disinfect with sodium hypochlorite, the active ingredient in bleach the pH will be raised closer to 7 making it easier to store for future use.
Surface water is any source of water that is on the surface of the earth. Lakes, rivers, streams, ponds, ditches and even puddles. The ocean is also surface water, but needs the additional step of desalination before acceptable for most uses. All surface water should be assumed to have pathogenic bacteria present. Even if you are on top of a mountain drinking right off of a glacier, assume bacteria are present. Glaciers also have a way of trapping air pollution, which will be released in to the melt water. The methods for treating surface water are numerous and diverse. I can’t list them all here. I discussed some of the basics in my post on purifying water. Before I drink any surface water I want it to be settled, filtered, and disinfected at the very minimum. Surface water collects and receives a lot of pollution. This is where a water test comes in handy. If you can, get some samples analyzed by a licensed laboratory. Knowing what is in your water is critical to know what needs to be removed. If a test is not possible, like it would be in SHTF scenario. Assume pathogenic bacteria are present. If it looks oily, assume there are hydrocarbons present. If there have been flooding for any reason recently assume a wide variety of contaminants are present. Boiling will remove volatile chemicals, but will leave behind heavy metals. As I continue to write blog entries I will go into more detail for the treatment of surface water.
This leaves ground water, most people in the world get their drinking water from ground water sources. This is the water that is found underground. There is however a class of ground water called GUDI, or groundwater under direct influence of surface water. GUDI sources should be treated like they are surface water as they will have all of the same issues. True ground water tends to be basic in nature, pH over 7. Higher pH comes from the long contact with minerals present underground. The soil above the aquifer acts a filter. In many cases the filtering ability of the soil is good enough to remove all pathogenic bacteria, but do not assume this to be true. Groundwater tends to be hard water as well. This is mostly due to dissolved calcium carbonate. Hard water has many health benefits, but can be detrimental to appliances. There are many places where ground water is pumped with zero treatment and is safe to drink. Even some public water systems only disinfect and distribute ground water. Some groundwater is contaminated with chemicals from nearby land uses. Look who your neighbors are, be wary of farms, gas stations, mines and heavy industry. Railway ties have also been known to leach chemicals into the surrounding ground. Other things to consider are the locations of buried waste storage, like septic tanks and municipal sewers. If these leak they can contaminate the surrounding ground water. The single greatest thing you can do to protect your ground water is to protect the area around your well. Don’t add anything or do anything you wouldn’t want to drink later within 7ft (2m) of your well. Planting a garden is a good way to mark the area around the well, just don’t use any pesticides or fertilizer.
Choosing a source of drinking water isn’t something to be taken lightly. If you have choice, consider yourself lucky. If you only have one option, consider yourself lucky. Make the best you can with what you have and do your best to treat your water before drinking it.