Contaminants that may be in untreated<unk>  include microorganisms such as viruses and bacteria; inorganic contaminants such as salts and metals; pesticides and herbicides; organic chemical contaminants from industrial processes and petroleum use; and radioactive contaminants.<unk>  depends on the local geology and ecosystem, as well as human uses such as sewage dispersion, industrial pollution, use of<unk>  bodies as a heat sink, and overuse (which may lower the level of the<unk> .
The Environmental Protection Agency prescribes regulations that limit the amount of certain contaminants in the<unk>  provided by public<unk>  systems for tap<unk> . Food and Drug Administration (FDA) regulations establish limits for contaminants in bottled<unk>  that must provide the same protection for public health. Drinking<unk> , including bottled<unk> , may reasonably be expected to contain at least small amounts of some contaminants. The presence of these contaminants does not necessarily indicate that the<unk>  poses a health risk.
Some people use<unk>  purification technology to remove contaminants from the municipal<unk>  supply they get in their homes, or from local pumps or bodies of<unk> . For people who get<unk>  from a local stream, lake, or aquifer, their drinking<unk>  is not filtered by the local government.
Toxic substances and high populations of certain microorganisms can present a health hazard for non-drinking purposes such as irrigation, swimming, fishing, rafting, boating, and industrial uses.  These conditions may also impact wildlife which use the<unk>  for drinking or as a 
Habitat.
Interest by individuals and volunteer groups in making local<unk>  observations is high, and an understanding of the basic chemistry of many<unk>  parameters is an essential first step to making good measurements. Most citizens harbor great concern over the purity of their drinking<unk> , but there is far more to<unk>  than<unk>  treatment for human consumption.
Statements to the effect that "uses must be preserved" are included within<unk>  regulations because they provide for broad interpretation of<unk>  results, while preserving the ultimate goal of the regulations. Technical measures of<unk> —that is, the values obtained when making<unk>  measurements—are always subject to interpretation from multiple perspectives.  Is it reasonable to expect a river to be pristine in a landscape that no longer is?  If a river has always carried sediment, is it polluted even if the cause is not man induced?  Can<unk>  be maintained when<unk>  quantity can not?  The questions that arise from consideration of<unk>  relative to human uses of the<unk>  become more complex when consideration must also be given to conditions required to sustain aquatic biota. Yet inherent in the concept of preserving uses is a mandate that<unk> ways must be much more than conduits for a fluid we might want to drink, fill our swimming pool with, or carry our wastes out of town
Water quality
Dental restorative materials
Organic chemistry
Health care
Nutrient
Mobile health
Biological system
Food chemistry