\These define drinking water in terms of microbial concentration , presence of metals and other elements in terms of their desired concentration.
TDS is not part of the primary drinking water specifications.Some of the drinking water specifications can be found atBIS Specification for drinking water in India:
Total dissolved Solids [TDS] in drinking-water originate from natural sources, sewage, urban run-off, industrial waste water, and chemicals used in the water treatment process, and the nature of the piping or hardware used to convey the water, i.e., the plumbing In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.
Therefore, the total dissolved solids test provides an qualitative measure of the amount of dissolved ions, but does not tell us the nature or ion relationships. In addition, the test does not provide us insight into the specific water quality issues, such as: Elevated Hardness, Salty Taste, or Corrosiveness.
Therefore, the total dissolved solids test is used as an indicator test to determine the general quality of the water. The sources of total dissolved solids can include all of the dissolved cations and anions, but the following table can be used as a generalization of the relationship of TDS to water quality problems.
The Environmental Protection Agency (EPA) establishes standards for drinking water which fall into two categories -- Primary Standards and Secondary Standards. primary Standards are based on health considerations and Secondary Standards are based on taste, odor, color, corrosivity, foaming, and staining properties of water.
There is no Primary drinking water standard for total dissolved solids, but the Secondary standard for TDS is 500 mg/L[Even the BIS standards says so] . These problems may be associated with staining, taste, or precipitation. With respect to trace metals, an elevated total dissolved solids may suggest that toxic metals may be present at an elevated level. It is important to keep in mind that water with a very lower TDS concentration may be corrosive and corrosive waters may leak toxic metals such as: copper and lead from the household plumbing. This also means that trace metals could be present at levels that may pose a health risk.