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

 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.

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.

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

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

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

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

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

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.

3 marks