Hello Bernie, Thank you for your question! According to Rinnai, you are able to use a tankless heater with well water as long as there is no excess mineral build-up. However, they did say that you should test the water before using and you will need to flush the system more often. Since this is an external unit, you will not need any venting materials. Below you will find my direct line in my signature. Give me a call if you have any additional questions, or when you are ready to place your order!