A method and system for irrigating a field adjacent a watercourse is disclosed comprising a plurality of pumps along the watercourse and measuring from time to time at a plurality of measuring locations the salinity, the pH, the temperature and the turbidity of the water. The measuring locations are different from the pumping locations. A real time salinity, pH, temperature and turbidity at the pumping locations is predicted from the measured values and the pumps selectively disabled or enabled on the predicted salinity, pH, temperature and/or the turbidity.