For saving the planet in any small way you can, avoid sprinklers and hose pipes in the garden. Use a watering can instead. That way, you can regulate the usage of precious water. Use up cooled waste water in the garden. Wash your greens over an empty bowl or pot so that the used water collects inside it. Then use it in your garden.
I discovered I could save enough water to wash all the plants in the garden by using up the water that washed my spinach!