Hi. Here are my suggestions towards your essay.
The cholera is one of disease that is caused ...if you want to tell the water which is contaminated, you can try to use "contaminated water rather than water contaminated."
The previous device to test water contaminated ...The device to test contaminated water or the device to test the water containing harmful materials.
disadvantages, like after ...
"like" is not conjunctions.
for implementation need very expensive cost.Prepositional phrase is not able to be the subject of sentence.
because use light for the chemical reaction to take place, also it is cheap ...
where is your subject here?when you are using the conjunctions, make sure that (the number of conjunctions = the number of sentence +1)
light which the red light indicate the contaminated water
You cannot use this adverbial clause here. try to use Noun Clause.
I hope it can be useful for you.
Goodluck and Keep Spirited.