Water Treatment Process

Corbalis Plant

Both the Corbalis and Griffith Plants use a six-step treatment process that ensures that its treated water is clean and safe to drink. In addition, Prince William Water continually monitors the water that is delivered to customers to ensure that it remains clean, safe and of the highest possible quality.

  • The first step is coagulation, which involves adding chemicals to the water. That causes small particles to adhere to one another, or coagulate.
  • The second step is called flocculation, in which larger particles called flocc form after coagulation.
  • Sedimentation occurs next when the heavy flocc settles to the bottom and is cleared away.
  • In the fourth step called ozonation, plant workers add a gas called ozone to destroy bacteria and other microorganisms as well as to improve taste.
  • From there, the water is filtered using granular activated carbon to remove any fine particles.
  • Finally, the sixth step is secondary disinfection, which involves adding chlorine to ensure a safe product is delivered to your home.
Photo: An aerial view of a drinking water treatment plant

At the City of Manassas treatment plant, raw water from Lake Manassas enters the water treatment plant where pre-filtration chemicals are added. These pre-filtration chemicals cause the particles contained in raw water to adhere to one another, making them heavy enough to settle out in the settling basins. After settling, water is filtered through layers of anthracite, gravel and silicate sand. As smaller suspended particles are filtered out, clear water emerges. After filtration, the water is disinfected with sodium hypochlorite, which is the primary disinfectant and is important to the treatment process because it helps to kill harmful bacteria, viruses and other microbial contaminants. Following disinfection, ortho-phosphate is added to prevent pipe corrosion.