We applied “water census database”, which we had estimated by a distributed model in standard grid cell, to the watershed management of Kasumigaura where watershed management has been proposed for its water quality improvement. We took up “sewage connection rate in local sewage area”as an item of watershed management, suggesting“E_{CR - 100/100P}” which means the effect of river water quality improvement by growing sewage connection rate as an incentive index to local people. Growing sewage connection rate from the cell where E_{CR -100/10OP} is larger in a same municipality, contributes to more effective improvement of river water quality in other cells. So that way is thought to be useful method of watershed management for getting local people being cooperative.