You live in the ground floor of a high rise apartment block. The over head water tanks which supply water to all the apartments are situated on the rooftop. When water flow through the taps in your apartment is low, you go to inspect the water level in the tank on the rooftop.
You check the water level in the tank and do the needful [get the tank filled]. How can you sort out the problem of checking the water level in the tank without going to the rooftop every time the water flow is low or water stops flowing?