What makes water safe to drink, how fresh water, sea water and sewage are treated, and the required practical on analysing and purifying water samples, with its hazards.
What you will learn
- Explain the difference between pure and potable water
- Describe how fresh water, sea water and sewage are treated
- Find the mass of dissolved solids per dm³ and compare samples fairly
- Plan the water practical and control its hazards
Pure is not the same as potable
In chemistry, pure means one substance only.
Potable water is water that is safe to drink: it has low levels of dissolved salts and microbes, but it is not pure.
Which treatment is used depends on where the water starts:
- Fresh water falls as rain and collects in the ground (in porous rock called aquifers) and in lakes, rivers and reservoirs. The UK has enough rain to rely on this.
- Sea water has far too much dissolved salt to drink. Dry countries with a coast may desalinate it.
- Waste water (sewage from homes, farms and factories) must be cleaned before it goes back into rivers.
Water for chemical analysis is distilled or deionised, because the ions in tap water could react or be mistaken for ions in the sample.
The rest of this lesson and its 14 practice questions are locked.
In this lesson
- Pure is not the same as potable
- Treating fresh water and sea water
- Treating sewage
- Required practical: analysing and purifying water
- Try it: Three samples, one fair comparison
14 practice questions, marked as you go; about 30 minutes in all.
Key terms
Pure, Potable, Fresh water, Aquifers, Sea water, Waste water, Filter beds, Sterilising, Desalination, Distillation
In this unit: Using resources
Making water potable and the water practical, life cycle assessments and recycling, phytomining and bioleaching, corrosion and materials, and the Haber process with NPK fertilisers, with every calculation worked.
- Potable water, waste water and the water practical
- Life cycle assessment and recycling
- Phytomining and bioleaching
- Corrosion, alloys, glass, ceramics, polymers and composites
- The Haber process and NPK fertilisers