In this video we will see how human beings have added to the natural water cycle. You can see that in one of our linked videos. By taking water from rivers for our use in towns and cities, humans began to interfere with the natural water courses long ago, wells have been dug to access clean water for drinking, the Romans built aqueducts to bring water to their cities. And nowadays we've built dams for irrigation and hydroelectricity, and we're taking a huge amount of water from natural sources to use in our homes and industries. Most people in industrialized nations take access to clean water for granted. However, more than one person in ten that's over 700 million people do not have access to clean water, and around three and a half million people die each year from water-related disease. The average Britain uses 150 litres a day, whilst each American uses 600 litres a day on average. In contrast, many sub-Saharan Africans get less than 20 litres of water a day, and two-thirds have no proper toilets. For some people, water is a precious and scarce resource. Only 3% of the water in the world is fresh. Of this, three quarters is locked up as ice in Antarctica and Greenland and Glaciers. Nearly another quarter is underground. Only 1% is above ground in rivers and lakes. We use the water mainly for irrigation of crops, and normally this needs no further purification. The next biggest user is industry. Sometimes, for example, in food preparation, very clean water is needed. Finally, there is domestic water. Some new housing estates in industrialized countries have a dual water supply, where grey water, collected from rain and from effluent from basins, baths and showers, is available for flushing and watering the garden, and the purified water is only used for washing and cooking. However, normally only one pipe supplies water to our homes, and this water has to be of drinking quality, and is purified on an industrial scale, at the waterworks. If you do not have piped water where you live, you might have access to a well. If the well has a brick or concrete wall in sides, the only water able to enter the well will be water that has had to seep through the surrounding rocks. This means that the water is likely to be pure and safe to drink. Pipe water from the waterworks for those lucky enough to have it, originally comes from rivers, lakes, reservoirs or underground aquifers. The grill will stop large floating objects, fish, etc, from entering the waterworks. Next, coagulants such as alum are added, which causes tiny particles in the water to cluster in lumps, which then settle in the sedimentation process. The filter is made of fine sand to capture any particles that are left. Finally, chlorine is added to kill any bacteria. If the water does not naturally contain fluoride ions, they are often added as sodium fluoride, as an aid to building strong teeth in those that drink the water. But for the 700 million people or so without access to clean water, small scale developments are beginning to help. If you are interested in these developments, look up clean drinking water for the world and learn about the life-straw biosan filters and many more. So to summarize, many people take clean water for granted, it comes in pipes filtered and chlorinated to make it disease-free from the waterworks. However, there are almost a billion people worldwide who do not yet have access to safe drinking water.