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City of Philadelphia

Drinking Water Treatment

PWD uses proven treatment practices and participates in groundbreaking research to provide drinking water that consistently exceeds EPA standards. Philadelphia’s drinking water sources are the Delaware and Schuylkill rivers.
The River
The source water comes from either the Delaware or Schuylkill River.

Natural Settling
After it has been pumped from the river, water is stored in reservoirs or basins to allow sediments to settle.
Chlorine is added to kill disease-causing pathogens.

Chemicals are added to the water to cause smaller particles in water to join together . This makes them heavier so that they will settle to the bottom of the basin.

The water is mixed to make sure the added chemicals are well blended and react with all of the smaller particles. The particles combine to form "floc," which settle to the bottom of the basin.

The newly joined particles (or "floc") settle by gravity and are removed from the bottom of the mixing tanks.

The water is drawn through filters, which remove finer particles still in the water for additional purification.

Final Treatment
Fluoride is added to help prevent tooth decay, and zinc orthophosphate is added to minimize corrosion activity between water and piping materials. Ammonia is added to reduce chlorine-like tastes and to maintain the chlorine in the water.

Water Storage & Distribution

Our water distribution system has the distinction of being one of the first in the country. When the Fairmount Water Works began operating in 1815, approximately 63 homes were connected by wooden mains to its reservoir, which was located on the hilltop now occupied by the Philadelphia Museum of Art.

Making it Safe: Drinking Water Treatment