Water can be used to defend from air by cooling temperature with ice making air harder to move. Water can be controlled in a stale mate fashion so it would have no power against a user. Ice can be fought against by increasing the ice temperature into water or mist. Plant bending can be stopped by expanding the plants and rupturing them. Also freezing them helps. Blood bending can be counteracted by bending your own blood. Earth bending can be made less lethal by turning ground into mud. Rock can be eroded by water if great force is used. Surrounding a projectile in water and then freezing it can be used to stop it by controling the ice. Metal can be rusted if you force the oxygen in the water to bond with iron. Rocks can be destroyed if boiling water is used and then quickly cooled. The same is true of metal that it can be warped with heat. Sand can be stopped by getting it wet. Magma can be cooled with water. Fire is doused by water. Water is a great conductor allowing redirection of lightning. Ice is a great barrier.