What should I do with my borewell?

Inside normal well of 40 feet we have taken a bore well at 200 feet depth

We used to have normal well its used to have salt water , and in summer water level will be very less, recently based on bore well drilling persons suggestion we have take a bore with 200ft depth in old well it self. We r getting good water from it. But around the casing also water is there in well. After reading questions and answers I am worried that this kind of arrangement will polute ground water. Any problems will come for borewells near to my bore well? Because our bore well is the depeset one in our village. Kindly advice what we have to do for not contaminating ground water . Water in well is ok not bore well casing.