Plant it to grow Water Bucket. Splash it around to make things wet. It can also scoop up water, though there's a good chance you'll just spill it. Butterfingers.
Water Bucket Seed price in Growtopia: sells for about 33/WL (median of 12 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: URRNO, I997, OTWKOPDES, EFQUY, ELBUB