Yeah it sounds stupid, but it is not as stupid as it sounds. This may just be working solution to a problem.
Your local water tower works the same way.
They pump it full at night when there is little water use, then allow it to flow during the day.
Otherwise there might be periods of low water flow in high demand time periods during the day.
Otherwise they would have to have pumps twice as large to handle peak flow in the daytime, which would sit idle at night
And it might be a way to “store” energy from Wind and Solar derived power. Use wind turbines to pump the water. Probably doesn’t have to be clean, regulated, power, too although the pumps might not like it.