Many people think that fresh water in our earth【 is not】（改成can not be）used up.They hold this opinion because the rainwater,well water,river water in our earth is abundant.In addition,with the development of science.People can use some equipments to【 make the seawater turn to fresh water】.（改成turn the seawater into the drinking water.）
Actually,the deposit of fresh water in our world is very 【short】 (改为limited).【The following are the reasons for the above idea】（改成the reasons are as followed理由如下,会不会好点,因为你这句话有点罗嗦）.First,a large number of people live 【in our earth】（改成on the earth,原句有点过于中式） and 【they need to drink all the time】（all the time 是一直的意思,表意有点过度了,直接说他们需要饮用水会更好,they need sufficient drinking water.）.Second,with the development of industry,a great quantity of fresh water 【are】 (改成 is )【used to produce】(改成used for producing).Furthermore,most people 【haven't awareness to protect 】（改成dont have the awareness of protecting）our fresh water and always waste it.
In order to solve 【the problem of global shortage of fresh water】(改成 this global-water-shortage-problem),we should take some【 measure 】(加 s )to make it.To begin with,every country must make a law to limit the industrial waste water 【】（加上or ）th rowed into the rivers arbitrary .Moreover,we should form 【have 】a（去掉have） good habit of protecting fresh water.
结构还算不错..句子有些嫌罗嗦,从句可以适当多用些.希望能帮到你