INTRODUCTION

Water is essential to support life. Water cleaning programs have been carried on for many years, but until the 1940s the clean-up process was simple. Cities located on rivers were expected to remove about thirty-five percent of the refuse that its citizens emptied into the water. The rest of the pollution was supposed to be purified by the river itself as it ran its course.

Since World War II, the nation's great increase in population has caused an increase in the amount of our waste materials. And to older types of pollutants such as drainage from coal mines, salt brine from oil wells, and wastes from paper and food industries, were added new chemical pollutants and radioactive wastes.

By 1980, industry in US needed more than 50 billion gallons of water daily. For hundreds of years, people have looked for ways to bring back the purity of water. History records how engineers, long before the American Revolution, trickled waste water over crushed rock, an attempt to copy the action of a stream purifying itself. In our modern world, we cannot wait for water to trickle over rocks. The job of purification must be done in a gigantic scale.

Over the years, the process of making old water into new is based on the same general plan. However, there have been inventions that are speeding and improving the work. One of these inventions is instruments with which chemists test water and quickly finds the amount of pollution that exists in it. This information helps them to plan how best to go ahead with the work.