Ielts taks1: the diagram show how rainwater is reused

The diagram below show how rainwater is reused
Summarize the information by selecting and reporting the main features and make comparisons where relevant

Please correct my mistakes i made and give a grade for my essay. Thanks very much.

The diagram shows details about progresses which people apply to reuse rainwater for personal purposes.

As can bee seen from the diagram, before human can use and reuse rainwater, there are some steps need to do.

Firstly, when rain falls, water is contained in Dam and then the water in Dam is pumped to Water Treatment Plant for treatment in order to create Drinking Water. This mount of water then is supplied to house for consumption. After the treated rainwater is used by people living in the house for household purposes such as drinking, cooking, cleaning etc, it becomes Household Wastewater and is moved to Wastewater Treatment Plant. At this plant, the water is completely purified and recycled to the house for consumption again and the rest is sent to river.

Secondly, when it rains, the rainwater running from the roofs of the houses is collected in a water tank. Because this rainwater resource is not cleaned, it is mostly used to water the garden.

Finally, we also can see in the diagram that the stormwater which rain falls to the ground flows through the pipe to the river.

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double verbs
there are some steps which need to do.

You have mentioned all steps in this diagram, but I'm not sure if you give your own opinion in this essay can be accepted.

Well, this task is meant to evaluate your report writing skills. So, you should adopt a more appropriate writing style for the purpose of reporting facts, trends and other data. When you reporting facts, your writing should be more concise, focused and informal. So avoid phrases like "Firstly, Secondly" etc.

Follow the approach Introduction, Overview and Details :)

Let me give a try for an overview:
Overall, the diagram shows how a drop of water flows from the source through the treatment process, which may be treated differently depending on the quality of the water which enters the plant.