its for aquarium so it is about 4 liters a day, but it fills it when the level drops so maybe 250ml in few hours and it ony stays on for couple sec ( maybe 10-15)
The vessel you pump the water out of would also have to be replenished on a regular basis - not so?
I have a similar need to yours and two mechanical rather than electronic solutions have come to my mind.
1) To install a square bucket (like a toilet cistern) with a float valve like they used in old toilets. You can take a pipe from this to your aquarium and never have to worry again.
2) The second idea I am toying with is to build a water dispenser similar to those used in bird cages but bigger (like an upside down bottle filled with water in a bowl). If the mouth of the bottle dries, more water runs out. The water reservoir could be far from your tank with the opening of the pipe at the level you want it in your aquarium.
At any rate I am interested to know how you keep the vessel you pump water from, filled with water