water+sources

Water Chemistry

Water is the most important chemical on Earth. Of all the water on the planet, 97% is found in the oceans. The other 3% is fresh water.

Most fresh water (70%) is stored as ice - in glaciers, ice caps, and snow. The next biggest source of fresh water is under ground, in aquifers (21%). Lakes, rivers and streams constitute a small percentage of all fresh water, and the remainder is in the atmosphere as water vapor.

Fresh water is extremely important for life; its sources are replenished via the [|water cycle].



__Fresh Water__

Fresh water is available to humans in a few ways:
 * wells and springs
 * natural and artificial reservoirs
 * rivers, lakes, or streams
 * ocean water desalinization
 * water recycling

Typically, major cities use artificial reservoirs, water recycling, and ocean water desalinization. Rural areas use wells and springs.

Each source has its issues, the chemistry of which will be examined here.

__Well and Spring Water__

Some well and spring water is clean, fresh, and chemical-free, requiring no extra treatment for its safe use. This is rare, however, and most wells require extra equipment to make the water useable.

Some issues with well water include:
 * pH (most ground water is acidic due to its flow through certain rock and through acid rain deposition); usually treated with caustic soda before filtration
 * iron (the most common issue with well water; dissolves into water from rock); usually treated with permanganate and then filtered out as a precipitate
 * hardness (dissolved calcium, magnesium, etc. causes scaling in pipes or ring-around-the-tub); treated with a softener containing salts that precipitate these ions
 * bacteria (especially common in farm lands from spreading manure); can be treated with UV light, chlorine or bromine
 * fertilizers/pesticides/herbicides (from lawn treatment, farm land, etc.); may not be removed by the above-mentioned techniques

The same or similar issues apply to spring water.

__Reservoirs__

Reservoirs can be natural or man-made, and are designed to hold large volumes of water, usually by damming a stream or spring. The water is then piped to a treatment facility and then sent to the consumer.

Issues with reservoirs include:
 * disruption of natural ecosystems where the reservoir was built
 * danger of flooding if the reservoir fails
 * acid rain deposition
 * algae, fish, or bird waste (cause of bad water odor; see bacteria, above)
 * dissolved minerals (see hard water, above)
 * [|trihalomethanes] (by-products of water chlorination or bromination)

Similar issues exist with using river, lake or stream water as a water source.

__Ocean Water Desalinization__

Salt water is the largest source of water on the planet, and most large cities are on the coastlines of oceans. Therefore, the purification of ocean water as a source of fresh water is sensible. There are currently over 13,000 desalination plants around the world, which produce 12,000,000,000 gallons of fresh water a day. However, this process has proven to be a difficult feat due to the following issues.
 * cost - desalinization requires a large and complex system, which uses large amounts of energy
 * distribution - pumping and piping the water to its destination can be difficult and costly
 * byproducts - concentrated salt water, solid waste, and warm water (brine) are potentially hazardous to the environment
 * ocean water intakes - dangerous to aquatic life
 * availability - due to the difficulty in transporting water, it is limited to communities close to the plants

__Water Treatment and Recycling__

Some major metropolitan areas are collecting waste water (including sewage), treating it, and reusing the water in order to reduce their dependence on reservoirs, rivers, or other major water sources. This is an environmentally sound approach to fresh water usage, but it has its disadvantages as well. These include:
 * cost of treating waste water to the point of safe consumption is high
 * disposal of solid waste is difficult
 * inability to remove potentially dangerous chemicals from the water:
 * very low concentrations of over-the-counter and prescription drugs have been [|found in drinking water]