Learning Objective Describe how we produce potable water To be able to: Describe how we produce potable water Key Words: Potable, drinking, dissolved

List ways that water samples could be different Monday, 20 May 2019 Potable Water Date and title in books. You need a pen, pencil & ruler. Starter Activity – 3 minutes List ways that water samples could be different

Describe ways to make water potable and compare it to pure water (F) Target 9-1 Identify what is meant by potable water (F/H) Target 4-9 Describe the ways water is collected and the issue with some of this water (H) Target 5-9 Describe ways to make water potable and compare it to pure water Extension: Application of Knowledge Target 8/9 Analyse data about water samples to identify what it could be used for Learning Outcomes

Potable Water Potable water is water that is suitable for humans to drink. It is not pure water in the chemical sense, as it contain small amounts of dissolved substances and bacteria.

UK Drinking Water We collect rain water, which has small amounts of dissolved substances in it (we call this fresh water) We collect it in river, lakes and reservoirs. We then make it potable.

Making rain water potable Pass the water through a filter bed Solids in the water, such as leaves and soil, must be removed. The water is sprayed onto specially-prepared layers of sand and gravel called filter beds.

Different-sized insoluble solids are removed as the water trickles through the filter beds. These are cleaned every so often by pumping clean water backwards through the filter.

Sedimentation 2. The water is then passed into a sedimentation tank. Aluminium sulphate is added to clump tiny particles together to make larger particles, which settle out more easily.

Filtration 3. The water is then passed through a fine filter, such as carbon granules, to remove very small particles.

UK Drinking Water 4. Sterilise the water This can be done using chlorine, ozone (O3) or ultraviolet light. e.g. Chlorine is added to drinking water to sterilise it. The chlorine kills microbes - including microbes that cause potentially-fatal diseases such as typhoid, cholera and dysentery.

Key questions Explain the stages of how rain becomes drinking water Suggest why the sterilisation stage of water purification is carried out last. Some data for a drinking water sample is shown below. Explain whether the water is potable.

No Fresh Water? If there is no fresh water, we will have to use salty water. Desalination removes the salt from the water, either by distillation or by reverse osmosis. It is expensive, as lots of energy is required.

Desalination is not modern science Desalination/distillation is one of mankind's earliest forms of water treatment, and it is still a popular treatment solution throughout the world today. In ancient times, many civilizations used this process on their ships to convert sea water into drinking water.

Desalination is not modern science Today, desalination plants are used to convert sea water to drinking water on ships and in many arid regions of the world, and to treat water in other areas that is fouled by natural and unnatural contaminants. Distillation is perhaps the one water treatment technology that most completely reduces the widest range of drinking water contaminants.

Desalination What are the disadvantages of producing drinking water using distillation? Suggest why Spain operates desalination plants whereas the UK does not.