How often should I put it on the base?

The Polti Moppy base serves two functions: it tops up the cloth with steam and eliminates the germs and bacteria gathered from surfaces. Put it back on the base when you feel that you need to dampen the cloth. For example, if it is not gliding as well over surfaces, or when you want to eliminate germs. The more you top up the cloth with steam, the damper it will be.