Water gives life. Polluted water causes all sorts of corruptions within the biota. Once the biota starts getting sick with parts of it dying away, the food web starts to disintegrate, and things and people start getting extinct. No life, dead planet. Welcome to mars.
It affects our planet... Duh!
Water pollution hurts our friendly fish like Nemo and the Little Mermaid!
Water helps our planet because it lets us drink and help animals