Drinking water
Drinking water is water that is intended to be ingested through drinking by humans. Water of sufficient quality to serve as drinking water is termed potable water whether it is used as such or not.  Although many sources are utilized by humans, some contain disease vectors or pathogens and cause long-term health problems if they do not meet certain water quality guidelines.  Water that is not harmful for human beings is sometimes called safe water, water which is not contaminated to the extent of being unhealthy. The available supply of drinking water is an important criterion of carrying capacity, the population level that can be supported by planet Earth.
As of the year 2006 (and pre-existing for at least three decades), there is a substantial shortfall in availability of potable water in lesser developed countries, primarily arising from overpopulation. As of the year 2000, 27 percent of the populations of lesser developed countries did not have access to safe drinking water. Implications for disease propagation are significant. Many nations have water quality regulations for water sold as drinking water, although these are often not strictly enforced outside of the developed world.  The World Health Organization sets international standards for drinking water.  A broad classification of drinking water safety worldwide can be found in Safe Water for International Travelers.
Typically water supply networks deliver a single quality of water, whether it is to be used for drinking, washing or landscape irrigation; one counterexample is urban China, where drinking water can be optionally delivered by a separate tap.  In the United States, public drinking water is governed by the Safe Drinking Water Act (SDWA).  Among other provisions, it protects the right of employees to report potential violations. 42 U.S.C. 300j-9(i).  Within 30 days of any retaliation, a whistleblower can file a complaint with the Occupational Safety and Health Administration (OSHA).
The standard test for bacterial contamination is a laboratory analysis of coliform bacteria, a convenient marker for a class of harmful fecal pathogens.  The presence of fecal coliforms (like Escherichia coli) serves as an indication of contamination by sewage.

# Metabolism
Water is essential for all life on Earth. Humans can survive for several weeks without food, but for only a few days without water. A constant supply is needed to replenish the fluids lost through normal physiological activities, such as respiration, sweating and urination. Water generated from the biochemical metabolism of nutrients provides a significant proportion of the daily water requirements for some arthropods and desert animals, but provides only a small fraction of a human's necessary intake.  There are a variety of trace elements present in virtually all potable water, some of which play a role in metabolism; for example sodium, potassium and chloride are common chemicals found in very small amounts in most waters, and these elements play a role (not necessarily major) in body metabolism.  Other elements such as fluoride, while beneficial in low concentrations, can cause dental problems and other issues when present at high levels. Water is essential for the growth and maintenance of our bodies, as it's involved in a number of biological processes.

# Access to drinking water
As a countrys economy becomes stronger (as its GNP per capita or PPP rise) a larger percentage of its people tend to have access to drinking water and sanitation.  Access to drinking water is measured by the number of people who have a reasonable means of getting an adequate amount of water that is safe for drinking, washing, and essential household activities.
It reflects the health of a countrys people and the countrys capacity to collect, clean, and distribute water to consumers.
According to the World Health Organization (WHO) more than one billion people in low and middle-income countries lack access to safe water for drinking, personal hygiene and domestic use.  These numbers represent more than 20 percent of the worlds people.  In addition, close to 3 billion people did not have access to adequate sanitation facilities.
While the occurrence of waterborne diseases in developed countries is generally low due to a generally good system of water treatment, distribution and monitoring, waterborne diseases are among the leading causes of morbidity and mortality in low- and middle-income countries, frequently called developing countries.
According to the United Nations over 1.1 billion people are currently without safe drinking water.  For details see data on the website of the Joint Monitoring Program (JMP) on water and sanitation of WHO and UNICEF.
The access to safe drinking water to the populations in several countries is listed below.
The main reason for poor access to safe water is the inability to finance and to adequately maintain the necessary infrastructure.  Overpopulation and scarcity of water resources are contributing factors.
Common places to find safe drinking water after a disaster are
- Water heater
- Household water pipes
- Toilet tank
Many other countries also lack in the amount of safe drinking water that they need to survive. Some of the countries have less than twenty percent of the population that has access to safe drinking water.  For example in Africa, with more than seven hundred million people, only forty six percent of people have safe drinking water.  The more populous Asia Pacific region with over three billion people, eighty percent of whom with access to drinking water, still leaves some six hundred and twenty seven million people without access to safe drinking water. 
The lack of water and the lack of hygiene is one of the biggest problems that many poor countries have encountered in progressing their way of life.  The problem has reached such endemic proportions that 2.2 million deaths per annum occur from unsanitary water - ninety percent of these are children under the age of five.   One program developed to help people gain access to safe drinking water is the Water Aid program.  Working in 17 countries to help provide water, Water Aid is useful in helping the sanitation and hygiene education to some of the world's poorest people.

# Drinking water quality monitoring
The standard test for bacterial contamination is a laboratory analysis of coliform bacteria, a convenient marker for a class of harmful fecal pathogens.  The presence of fecal coliforms (like Escherichia coli) serves as an indication of contamination by sewage.