Answer: Option (c) is the correct answer.
Step-by-step explanation:
Wasteful use of water means using water unnecessarily or without any need.
So, when we take a shower rather than a bath then it means we are using water for bathing and not wasting it.
Watering the garden with recycled water is also not wasting of water as we are reusing the used water.
Running dishwashers before they are completely full is a wastage of water because unless the dishwashers are not completely full the water will flow out and it is a wastage of water.
When we replace high-flow shower heads with low-flow shower heads then it means we are minimizing the flow of water and it is a conservation of water.
Therefore, we can conclude that out of the given options running dishwashers before they are completely full is the most wasteful use of water.