To change a plants water settings go to the plants blueprint so for example the BP_TomatoPlant and select the BP_PlantComponent in the Components panel, then in the Details panel and inside the Plant Settings Category find the Water category like the image below.
Here you can change this plant’s water settings, you can hover your mouse over each settings name to get a tooltip with more info about each setting.
You can enable or disable the Use Water setting to remove the plants need for water.
You can also set the plants Max Water which is the maximum amount of water the plant can store, you can also change the plants Starting Water which is the amount of water the plant begins with when placed or when the game starts.
Water Usage Time is how often a plant consumes its water in seconds and the Water Amount is the amount of water that will be used.
You can enable or disable the Show Water Usage UI this will remove the water usage panel from the plants UI.
You can set the plant to take damage when it has no water, this can be enabled or disable using the Use No Water Damage setting.
No Water Damage Time controls how often the plant will take damage in seconds and the No Water Damage is the amount of Damage the plant will take when it has no water.
Water can effect how fast the plant grows and how fast the vegetables grow. This uses the Growth Multiplier setting, if set to 0 having water wont effect the plants growth speed, if set to 0.5 the plant will grow 50% faster then its normal speed, this effect stacks with other stats grow multipliers.