Explain why it is important to ensure that fresh water sources used for potable water have low levels of dissolved salts and microbes.

It is important to ensure that fresh water sources have low levels of dissolved salts and microbes because high levels can pose health risks to consumers and affect the taste and quality of the water. Dissolved salts can lead to health issues and require additional treatment, while microbes can cause diseases.

A strong answer should directly address the approved learning objective to describe how fresh water sources are selected to produce potable water in the UK. This question belongs to Potable water within Using the Earth's resources and obtaining potable water, so the response should use that exact curriculum context rather than a generic statement. The answer is correct when it names the key idea, explains the link to potable water, and keeps the wording specific to AQA GCSE revision.