A visitor centre collects fresh rainwater in an open storage tank. The concentration of dissolved salts in the water is low enough for potable water.
The water is passed through a filter bed containing layers of sand and gravel.
| Measurement | Before the filter bed | After the filter bed |
|---|---|---|
| Mass of suspended insoluble particles in 100 cm3 | 240 mg | 8 mg |
| Mass of dissolved salts in 100 cm3 | 18 mg | 18 mg |
| Number of harmful microbes in 100 cm3 | 620 | 590 |
Use the information in the table to explain how the filter bed treats the water and what further treatment is needed before the water can be potable.
87 exam-style questions on AQA GCSE Chemistry 10.1 Using the Earth's resources and obtaining potable water, covering 10.1.1 Using the Earth's resources and sustainable development, 10.1.2 Potable water, 10.1.3 Waste water treatment, and 10.1.4 Alternative methods of extracting metals. Each one has a worked solution and a mark scheme showing where the marks go.