Waterfalls and streams need a mains water supply.
The first time, on discussing creating a garden pond, the customer carefully explained where the mains water supply was “as I would need it” I was taken aback; but it has happened now a number of times. The logic I presume is that as there is water running it must be from the mains. To clear up any confusion the water is circulated by an electric pump. Using the water mains wouldn’t work for a number of reasons. Tap water contains chemicals such as chlorine and fluorine which are added that could harm the plants and fish, if you’re constantly adding more and more water from the mains where will the excess go to, what is your water bill going to be, what happens as the water pressure goes up and down, what’s going to happen to the water pressure in the house and a domestic water supply does have sufficient water pressure or flow rate for all but the smallest water feature.