If you are in your RV Regularly, every two to three days. This will provide the softest water and best results, as well as keep the resin bed active in the softener which will help it last longer. If you only use your RV occasionally, it is better to recharge it before you leave and then every couple of days as needed, as you most likely won't experience a large shift in the quality of your water like someone who lives in their RV would.