Some fountains splash more than others and need to be monitored regularly. Most fountains, however, need only to be topped-up every few days, depending on the humidity, location, etc. Dry climates will cause more rapid evaporation, and locations with full sunlight will also require more frequent attention. The general rule is to try to keep your fountain at least ¾ full, but most importantly, to ensure the pump is fully submerged at all times.