Not all water is safe to drink. Water in lakes and rivers can be polluted. It can have harmful chemicals or germs that cause disease. Long ago, many people living in cities got sick or died from drinking dirty water. Scientists have learned how to clean, or purify, drinking water. They learned that boiling water could kill germs. They learned that adding certain chemicals could kill germs. Engineers learned how to keep dirty water in sewers, away from drinking water. Governments passed laws to keep factories from polluting water. People still get sick from drinking polluted water. Many poor people still do not have pure drinking water.
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