Question

About 97% of all the water on Earth is salty water in the oceans.

In a model, 5000 L of water stands for all the water on Earth. About 3% of it is fresh water. Of this fresh water, about 69% is ice, about 30% is groundwater and the rest is surface water in lakes, rivers and swamps. How many litres of the model stand for surface fresh water?

A school in Jaipur decides to harvest rainwater from its flat roof. The roof area is 200 square metres and the average yearly rainfall there is about 0.8 m (800 mm). The collected water is stored in an underground tank and used for gardening and toilets. The students also fix leaking taps and put up posters on saving water. (Use: volume of rain on roof = roof area × rainfall height; 1 cubic metre = 1000 L.)