The basin & pump supply water up thru the Waterboulder to flow down ver the Waterboulder. The basins come in a 42” diameter x 17” high, which will support a Waterboulder(s) up to 2,500 pounds and a 72” diameter x 17” high, which will support a Waterboulder(s) up to 4,000 pounds. The submersible pumps and pump kit accessories are sized to meet the needs of each water boulder