first paragraph:how can we solve the problem
second paragraph:why people widely think that fresh water is infinite?there are some reasons.F the plenty of rainfalls.S the infinitely minable wells (其实井和雨不是无尽的,你最好多查查关于水资源的资料),第三个就不要了吧,你用了太多量词了 river fall 是水位,不是水流.All above make people think that we have inexhaustible fresh water.nevertheless,we are short of fresh water,the development of chemical and electrical industry etc.caused severe water pollution.(这里也不知道帮你改什么好,总之别用tend to)
Now,we should take measures on the water pollusion.e.g.用你写的吧