on the contaminating agents and the probability 

 of peak loading of contaminants in the raw water 

 source. Wherever practical, comments on monitor- 

 ing needs are included along with the appropriate 

 recommendations for criteria in this report. 



Monitoring water quality 



Historical water quality data should be reviewed 

 when considering the type, location, and frequency 

 of sampling. If such data are not available, a sys- 

 tematic sampling program to provide background 

 information may be necessary. Continuing water 

 quality data are necessary to evaluate changes 

 which may occur with time. By Executive Order 

 [Bureau of the Budget Circular A-67 (1964)], 

 the Department of the Interior was given responsi- 

 bility to coordinate collection of both water quality 

 and quantity data and to design and operate a na- 

 tional network for these purposes. 



Most hydrological, climatic, and quality vari- 

 ables can be obtained and recorded or transmitted 

 in real-time at both remote and nearby locations 

 using sensors, transducers, and telemetering de- 

 vices available or under development. Improved 

 sensors, however, are needed for most variables, 

 and continued improvement of entire monitoring 

 systems is desirable. 



In interpreting water quality characteristics, 

 consideration should be given to the procedures 

 used in measuring them. This report, therefore, 

 contains references to accepted chemical and bio- 

 logical analytical procedures. One should recognize 

 that these will be continually changed and im- 

 proved. As new methods are introduced, results 

 should be correlated with those obtained by pre- 

 viously accepted methods. 



Scope and objectives of the report 



This report gives consideration to water quality 

 criteria of concern to agricultural users. The ob- 

 jectives are to describe limits of use for agricul- 

 tural purposes. Wherever possible, criteria are ex- 

 pressed as quantitative ranges. Some of these are 

 necessarily broad because of lack of information 

 or of wide flexibility in specific uses; others which 

 may be better understood or more critical, are 

 narrow. Where quantitative estimates are presently 

 impossible, general criteria characteristics are de- 

 scribed. In suggesting values for criteria, considera- 

 tion has been given to both health and economic 

 factors affecting the farmer, food processors, and 

 the ultimate consumers. 



summary 

 and key criteria 



114 



