The water treatment industry employs a number of chemical and mechanical means to "tailor" water to meet the needs of customers. Of the half-dozen processes, the two basic ones are clarification and filtration.

Clarification is the removal of suspended matter in raw river or lake water. Chemicals are often added to cause the small particles to floe or bunch up, so they will settle out quickly in the bottom of a large tank. As the floe settles, it forms a blanket. The blanket also acts as a filter, trapping even finer particles as the water moves slowly through.

After clarification, the water is filtered, through a bed of fine, clean sand or other substance to remove most of the foreign matter that remains. Filtration is achieved by a gravity system, or in some cases, the water is put through filters under pressure in closed tanks.

Q. Underline a general statement which alerts the reader to the work of the water treatment industry