Our area is sandy with water table 3 metres from ground. The height of our building overhead tank is 50 feet from ground level. The existing borewell is 45 feet deep with 4" dia pvc casing. Of late the yield is very low. The rock in our area is 70 feet depth. Can we have a 1 foot dia bore well upto the rock depth with 1"x!" suction jet pump. Can this improve yield? Fill the tank faster? Our doubt is 4" dia borewell is not able to improve the yield. Moreover the slots int casing pipes are choked as the bore well is quite old and perhaps they had used nylon net around the casing pipe. Would appreciate your clarificiation.