Sampling is necessary to obtain reliable data on chararcterisation and qualification of any type of waste, waste water, stream water etc. Therefore a scientific approach is needed during sampling and analysis to get maximum details.

Factors that can be considered in the design of sampling program are :

1. Total number of samples: The number of samples required depends upon the objective of the program, amount of time and effort. It is better to concentrate on well defined, frequent and intensive sampling.

2. Points of collection: Sampling point should be selected with great care & special consideration be given to source of pollution, dilution by branch streams, changes in surrounding topography. A minimum of 4 stream station are recommended.

3. Method of collection: In deeper streams it is necessary for sample to form composite portions taken from depth level of 0.2 & 0.8. When stream flow remains quite steady, equal portion of each sample may be composited by analysis. A standard type dissolved oxygen sampler is recommended for collecting most samples.

4. Data to be obtained : The scientific collection of data for stream analysis may be divided into 3 major categories. a) Hydro logical factor. b) Sources of pollution. c)Watercourse sampling The type of data to be obtained depends on objective of survey and amount of money and time available.

5. Frequency: Samples should be collected as frequently as possible to provide a representative total sample.