Water Quality Standards

International Organization for Standardization specification for water for laboratory use ISO 3696: 1995
This standard covers three grades of water as follows:
Grade 1 
Essentially free from dissolved or colloidal ionic and organic contaminants. It is suitable for the most stringent analytical requirements including those of high performance liquid chromatography (HPLC). It should be produced by further treatment of grade 2 water for example by reverse osmosis or ion exchange followed by filtration through a membrane filter of pore size 0.2µm to remove particle matter or re-distillation from a fused silica apparatus.
Grade 2
Very low inorganic, organic or colloidal contaminants and suitable for sensitive analytical purposes including atomic absorption spectrometry (AAS) and the determination of constituents in trace quantities. Can be produced by multiple distillation, ion exchange or reverse osmosis followed by distillation. 
Grade 3
Suitable for most laboratory wet chemistry work and preparation of reagent solutions. Can be produced by single distillation, by ion exchange, or by reverse osmosis. Unless otherwise specified, it should be used for ordinary analytical work.

American Society for Testing and Materials (ASTM) D1193-2006 Standard specification for Reagent Grade Water

This specification covers requirements for water suitable for use in methods of chemical analysis and physical testing, the choice of one of the various grades being designated by the method or the investigator.

Key:*Requires the use of 0.2µm membrane filter 
** Prepared by distillation
*** Requires the use of a 0.45µm membrane filter

When bacterial levels need to be controlled, reagent grade types should be further classified as follows:

Clinical and Laboratory Standards Institute (CLSI) (C3-A4)

Type I water must be free of particulate matter larger than 0.2µm 
Resistivity of Type I must be measured in-line

Pharmacopoeia standards
Separate pharmacopoeia are produced by a number of authorities, notably in the USA and Europe. Each specifies materials, including water, to be used in medical work. The standards for purified water are similar in each case. Extra criteria are set for water required for sterile applications. The standards for purified water given in the European Pharmacopoeia (EP) and in the US Pharmacopoeia (USP) are summarized below. Water for injection has stringent bacterial/pyrogen criteria and methods of preparation are specified.

Pharmacopoeia requirements for purity of “purified water”

 Water for analytical laboratory use-Specification and test methods (China GB/T 6682-2008)