3.4. Characteristics of Pure Water

 Webster defines pure water briefly as: "The liquid which descends from the clouds in rain, and which forms rivers, lakes, seas, etc. Pure ordinary water (H₂0) consists of hydrogen (11.1888 %) by weight and oxygen (88.812 %). It has a slightly blue color and is very slightly compressible. At its maximum density at 39.2 °F or 4 °C, it is the standard for the specific gravities of solids and liquids. Its specific heat is the basis for the calorie and the B.T.U. units of heat. It freezes at 32 °F or 0 °C".

However; in reality "pure water" (H₂0) occurs so rarely, that it can be called a non-existent liquid. Even the term "pure water" is vague having different implications to individuals in different fields. For example "pure water" is a sterile liquid for bacteriologists that do not contain any living bacteria in it. The chemist, on the other hand, might classify water as "pure" when it possesses no mineral, gaseous or organic impurities. Therefore, "pure water" as described is likely to be found only in laboratories and only under ideal conditions.

Environmental Protection Agencies (states/regional/territorial) and national regulatory bodies provide practical standards for water in terms of its suitability for drinking for aesthetic considerations in Water Regulations. In these regulations, the authorities commonly take into consideration adequate protection of water against the effects of contamination, both through natural processes and through artificial treatment. The standards in these regulations list requirements for bacterial count, physical and chemical characteristics.

Any source of water to meet basic requirements for a public water supply needs some form of treatment. In general, water to be used for public water supply;

• Should contain no disease-producing organisms.
• Should be colorless and clear.
• Should be good-tasting, free from odors and preferably cool.
• Should be non-corrosive.
• Should be free from gases, such as hydrogen sulfide and staining minerals, such as iron and manganese.
• Should be plentiful and low in cost.

A comparative table of both WHO and EU drinking water standards can be found below (Table 3.1);

Table 3.1. WHO and EU drinking water standards

1. Desirable: Less than 5 NTU
2. Desirable: 6.5-8.5
3. Desirable: 15 mg/l Pt-Co
4. Desirable: Less than 75% of the saturation concentration
5. Desirable: 150-500 mg/l
6. Desirable: 0.3 mg/l

(Ref:http://www.lenntech.com/who-eu-water-standards.htm)

To read more;

• Parameters of Water Quality, Interpretations and Standards, (Environmental Protection Agency (EPA)
• Guidelines for Drinking-water Quality FIRST ADDENDUM TO THIRD EDITION Volume 1 Recommendations, World Health Organisation (WHO)
• National Water Quality Management Strategy, Australian Drinking Water Guidelines 6, 2011, Version 3.1 Updated March 2015, Australian Government, Netional Health and Medical Research Council, Natural Resource Management Ministerial Council
• Assessing Microbial Safety of Drinking Water, Improving Approaches and Methods, Published on behalf oft he World Health Organisation for Economic Co-operation and Development (OECD) by IWA Publishing.