Water dumping involves building a bridge above the opposing team's planet and dumping bucketfuls of water onto it. This strategy ruins cobble generators, knocks off torches, washes beds out, and just generally fucks up everything. Alternatively lava can be used, just make sure you don't pour it all over yourself and incinerate everything you were carrying, or pour the lava over the other teams spawn pool and get disqualified. If you do decide to use water an effective way to use the same waterfall while preventing the enemy from climbing up is to break the few surrounding blocks around the water source. Even if an enemy were to reach the top of the waterfall, there would be no blocks for them to jump onto, effectively one-waying the waterfall.