We always recommend Distilled water. Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.
The use of distilled water will dramatically cut down on the maintenance of your fountain as heavy metals, minerals and calcium have been removed. It will also ensure the longevity of your pump as well. If you can't get distilled water we suggest a filtered drinking water. Always try to avoid the temptation of using tap water. Tap water is full of hard minerals and often chlorinated. Using tap water will cause the quick build-up of hard water deposits no only spoiling the beauty of your fountain but potentially impacting the way it runs. These deposits can also build up on inside the pump as well causing it to work harder. "O' rings inside the pump and valves will become brittle with chlorinated tap water so we encourage you to "just say no" to tap water.