Positive results obtained from an artificial rain experiment in Israel are the major motive for the proposed extension of the Israel National Water System. Should the system be extended while the artificially induced rain increment, though highly probable, is not definitely proven? The decision maker is confronted with the choice between two alternative policies: to extend the system or not to extend it. Either policy will yield a certain expected value that is determined by the probability of increasing the water yield of Lake Kinneret by cloud seeding. The probability of ‘no increase’ that would give equal justification to both policies seems considerably higher than the no-increase probability indicated by the findings of the artificial rain experiments, and thus the policy of ‘extension’ appears to be preferable.