There is an 8000 liter water tank on top of my house which provides water for the house.
Bacteria, fungi, algae, etc. often start developing in the tank, giving unpleasant smells, etc.
The water is ground water that we pump up there with our own pump.
The tank is made of concrete and covered with a steel lid.
Nobody is drinking or cooking with the water. It's used for stuff like laundry, showers, washing dishes, etc.
What can I do to prevent these unpleasant qualities of the water? It's very hot here (like 40 celsius in the shade), and the water tank is in the baking sun.
My landlord is unlikely to want to make any large investments. Therefore, cheap solutions are a plus.
Edit: Several answers have suggested chlorination, and it seems like the best option. But I live in rural India and it's difficult to find chlorine here. Bleach, though is readily available. Does it seem suitable? I've asked this as a separate question on Chemistry SE.