Band 5+: You should spend about 20 minutes on this task. The diagram below shows how salt is removed from seawater to make it drinkable. Summarize the information by selecting and reporting the main features and make comparisons where relevant. Write at least 150 words.

The diagram illustrates the removing salt process from sea water to drinkable water.

Overall, there are four primary stages of purifying process, begin with taking in salt water from the sea that the quality of water not be able to drink pass through the operations until the last stage of distribution to the water supply system.

Starting at the sea, the intake of salt water goes through the pipe to the first stage, salt water get in the pre-treatment filter, some part of water go to the filtering backwash and returned to sea. Then water force through membrane at high pressure, the impurities in water will be deliberately extract in this filter, the water molecules and salt separate within the filter, the sea water concentrate return to the sea. Next, the water flow to post-treatment with lime chlorine and fluoride for improve the quality of water before store them in the storage and distribute to the last stage integrating water supply system.