In the agricultural sector, groundwater is being polluted through influx of a part of nitrogen from Nitrogen fertilizers. Water contamination threatens villagers' health, because they provide their drinking water from wells nearby farms.. In this paper contingent evaluation method has been employed to estimate water quality changes, as reflected by 310 respondents from some fore cities of: Rasht, Bandar anzali, Langrood and Astaneh ashrafieh from Gilan Province .The number of sample was assessed by use of purposely method and classified multistage. Results indicate that 54% of farmers support financial participation to improve water quality. With water contamination decline, the expected value of Willingness To Pay (WTP) is estimated to be 394069 and 437855 rials per family and per hectare. Also the average Willingness To Accept (WTA) are 13202501 and 13276136 rials per family and per hectare. Income classes and education specify the maximum and the minimum values of water quality changes, respectively.According to the results, balance between water quality conservation and durable economical production, will be achieved by implementing subsidiary support policies, changing distribution policies of nitrogen fertilizers to policies that improve livelihood of farmers, and as well, decrease water contamination from other incoming pollutants. JEL Classification: Q25,Q51,Q53.