Why is it necessary to treat waste water before it is released into the environment?

Waste water must be treated to remove harmful substances, such as organic matter and microbes, that can pollute water bodies and harm aquatic life. Untreated waste water can lead to environmental degradation and pose health risks to humans and wildlife.

A strong answer should directly address the approved learning objective to explain why waste water must be treated before it is released into the environment. This question belongs to Waste water treatment 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 waste water, and keeps the wording specific to AQA GCSE revision.