2. BOREHOLE - a deep, narrow hole made in the ground, especially to locate water or oil. Providing people with clean drinking water is a major issue all over the world.  Water that comes from boreholes is usually fairly clean  It is filtered as it passes through the rocks around the borehole  Normally all we need to do is sterilise this water with chlorine to make it safe enough to drink.  Chlorine kills microbes in the water

3.  However water that we take from rivers and reservoirs needs more treatment than this.  This treatment involves several physical and chemical processes  The water source is chosen so that it contains as few dissolves chemicals as possible.  The water than passes through 5 stages.

5. RESERVOIR FILTER (made of fine sand; removes mud and grit) SCREEN (metal bars close together) catches large leave and twigs SETTLEMENT TANK – sand and soil settle out ALUMINIUM SULPHATE AND LIME ADDED – small particles of dirt clump together and sink to the bottom. Sludge is dumped into landfill. CHLORNE ADDED – kills bacteria pH OF WATER CHECKED – water must be neutral. The water is then stored in large tanks.

14. FILTER JUGS IN YOUR HOMES As water trickles through the top part of your jug it then passes a water filter The water filter contains  activated carbon  an ion exchange resin and  silver

17. PURE – OR JUST FIT TO DRINK  Eventhough water goes through a water jug it is NOT pure as it still contains dissolved substances.  But despite this it is still fit to drink  We can get pure water by distilling it  Distillation involves boiling the impure water; the liquid water turns to steam  Then it cools down and condenses into pure liquid water

20. WATER ISSUES TO SOFTEN OR NOT SOFTEN?  People in hard water regions want to soften their water  The money they spend on water softeners and filters for their jugs and repair costs to get rid of limescale cost a lot of money  However, some people disagree since hard water is beneficial to health  Ion exchange columns replace Mg 2+ and Ca 2+ ions, which make water hard with Na + ions.  Na+ ions are not good for the heart and have been linked with high blood pressure

21. CHLORINE IN WATER  Chlorine kills bacteria in water  But the amount of chlorine in water must be monitored as chlorine compounds are toxic  Ozone (a gas) can be used as an alternative to using chlorine to kill microbes in water

22. FLUORINE IN WATER  Fluoride ions (F - ) can protect against tooth decay  It is added to water for exactly that reason  However there are advantages and disadvantages: ADVANTAGES  It has not been proved for 50 years that fluoridated water causes harmful affects  The effect of fluoridation as shown 30% reduction in cavities on teeth  It has been shown that you are 5x more likely to have tooth decay in areas where there is no fluoride ions in water  We need fluoridation to protect teeth as many people in areas of poor dental hygiene do not visit the dentist regularly  The bacteria associated with tooth decay also cause some types of heart disease so fluoridation protects us from that  Fluoride ions are only added in very small amounts

23. DISADVANTAGES  Fluorosis is a condition caused when children have too much fluoride.  White streaks or tips appear on their teeth  These are deposits of Calcium fluoride  This could be a sign of other changes in the bones  Some studies have shown that excess fluoride can weaken bone, increasing the number of fractures and bone cancer  It is ethically wrong to give people fluoride treatments that they have not consented to. People have the right to choose.  Some studies show that excess fluoride affects the brain. Producing learning difficulties  You can`t set safe limits of fluoride because you cant control peoples intake.

25. 3 marks