which one?

ok i am doing 1000 word S.A for science and i have to choose

either:

1. why is water so important fot life?
2. what are the different effects of water pollution?
3. how can we contrl the water pollution? (individual and gevernment level)

ok i am not sure wat to do and i have alot other h.w to do and i want to get this out of the way (it s due in 4 days!)so which one do u think is the easiest hoặc the the smartest?