Introduction 

Water is one of the most important and basic natural resources.  Water is not only one of the most essential commodities of our day-to-day life, but the development of this natural resource also plays a crucial role in economic and social development processes. While the total amount of water available in the world is constant and is generally said to be adequate to meet all the demands of mankind, its quality and distribution over different regions of the world is uneven and causes problems of scarcity and suitability.  It is therefore imperative that man develops, uses and manages this scarce commodity as rationally and efficiently as  possible. In order to execute this task, accurate and adequate information must be available about the quality of the this natural resource under constantly changing human pressures and natural forces.  

Water quality management is for a great deal controlled by authorization of discharges of dangerous substances for which monitoring of discharges, effluents and influenced surface water is essential.  On national and state levels, we have several policies and regulation like Water (Prevention and Control of Pollution) Act, 1974 to regulate pollution discharges and restore water quality of our aquatic resources including the prescription of monitoring activities (Box-1,2 and 3). Under Water Act, 1974, pollution control boards were created, who are responsible for implementation of its provisions. One of the important provision of the Water Act, 1974 is to maintain and restore the ‘wholesomeness’ of our aquatic resources. To define the level of ‘wholesomeness to be maintained or restored a system of water use classification was developed. Under this system water uses are classified in 5 classes (Box-4). If a water body or its part is used for multipurpose, then the use which demands highest quality of water is designated as ‘designated best use’ and accordingly water body or its part is designated. Now through regular water quality monitoring existing water quality is assessed and compared with the desired quality as identified under designated best use class and gaps are identified. Based on the identified gaps the water body or its part is identified as polluted.   Water quality monitoring is one of the first steps required in the rational development and management of water resources. In the field of water quality management, there has been a steady evolution in procedures for designing system to obtain information on the changes of water quality.  The ‘monitoring’ comprise all activities to obtain ‘information’ with respect to the water system.  

Water quality monitoring is a complex subject, and the scope of it is both deep and wide. Water quality monitoring has a direct relation with chemistry, biology, statistics and also economics.  Its scope is also related to the types of water uses and functions which are manifold and the nature of the sources  of water such as surface water (rivers and lakes), sea water groundwater. 

The Central Pollution Control Board (CPCB) is an apex body in the field of water quality management in India. For rational planning of any water quality management programme, CPCB needs to know the nature and extent of water quality degradation. Therefore, a sound scientific water quality monitoring programme is prerequisite. Realising this fact,  water quality monitoring was started in 1976 by CPCB with 18 stations on the Yamuna river. The programme was gradually extended. Today, there are 1032 monitoring stations in the country spread over all important water bodies. 

Water Quality

Water quality is a complex subject, which involves physical, chemical, hydrological and biological characteristics of water and their complex and delicate relations. From the user\'s point of view, the term \"water quality\" is defined as \"those physical, chemical or biological characteristics of water by which the user evaluates the acceptability of water\". For example for drinking water should be pure, wholesome, and potable. Similarly, for irrigation dissolved solids and toxicants are important, for outdoor bathing pathogens are important and water quality is controlled accordingly. Textiles, paper, brewing, and dozens of other industries using water, have their specific water quality needs. 

What is monitoring ?

Webster\'s dictionary defines monitoring as (1) to check and sometimes to adjust for quality or fidelity, (2) to watch, observe or check, especially for a special purpose, (3) to keep track of, regulate or control (as a process for the operation of a machine). Note that both (1) and (3) involve adjustment, regulation, or control, which fit well with the various types of monitoring information. A distiction can be made between different monitoring activities: 

Survey: short term observation(s) on water quality (in present context) to fulfil definite objective(s); 

Surveillance: a continued programme of surveys systematically undertaken to provide a series of observations in definite time period; 

Monitoring: continuous surveillance undertaken to fulfil set of objectives.