Do you have water-logged areas and alkali spots on your land? How about similar areas and spots on your neighbor's land upstream? The way water is used upstream from your intake, with the possible exception of that used for power development and navigation, has a great deal to do with the quality of water which reaches your farm. The way you use water on your own farm for irrigation may change the water quality in relatively short stretches of a river. Growing plants require large quantities of water, but as they grow they do not use much of the minerals which are dissolved and carried in irrigation water. As a result, these dissolved solids become concentrated in the water which remains unused. Drainage from unimproved and irrigated areas (as desirable as this may be for the lands drained) will increase the dissolved solids content of the stream into which these drainage waters flow.
Additional publication details
Irrigation and water quality: Part 1--how dissolved solids increase in irrigation water