Raw water from the Mississippi River is pumped to the Carrollton Water Purification Plant from both the Oak Street River Station and the Industrial Avenue River Station. The purification process begins with the addition of a coagulant chemical, commonly called polyelectrolyte, at each river station. Polyelectrolyte consists of long chain molecules carrying electrical charges that cause fine suspended particles to coagulate, or gather together into larger particles. Water treated with polyelectrolyte travels through several large pipelines from the river pumping stations to the water plant.

As the raw water enters the Carrollton Plant, it is treated with ferric sulfate and lime. Ferric sulfate is also a coagulant chemical, and it is used to aid the polyelectrolyte in the raw water clarification process. Lime, also known as calcium oxide, is used for pH adjustment, softening, and corrosion control.

After the raw water has been treated with polyelectrolyte, ferric sulfate, and lime, it is gently mixed by large mechanical paddles in two flocculation basins where the suspended particles gather together into larger particles. The flocculated water then travels into two (2) primary settling basins where the particles settle. The settled particles form a sludge layer on the bottom of each primary settling basin. This sludge is pushed into sumps by traveling mechanical rakes, and is then removed from the basins through a series of valves and pumps.

The clarified water then exits the settling basins, and is disinfected by the addition of free chlorine. Anhydrous ammonia is added shortly thereafter, producing chloramine. Chloramine is a compound produced by reacting free chlorine with ammonia, and is used for residual disinfection.

Chloraminated water then enters large secondary settling basins, allowing additional settling time for suspended particles and disinfection contact time. After the water exits the secondary settling basins, it is treated with sodium hexametaphosphate and fluorosilicic acid. The sodium hexametaphosphate is used as a sequestrant, which holds the lime in solution keeping it from depositing on the filter or the media. The fluorosilicic acid is used to add fluoride to the drinking water to aid in the prevention of dental cavities.

The final step in the purification process is filtration through 44 rapid sand filters. These filters consist of graded gravel topped first with a layer of sand and then with a layer of anthracite. After filtration, the purification process is complete, and drinking water is pumped out to customers.

The Sewerage and Water Board also operates a water treatment plant on the west bank of the Mississippi River in Algiers. The purification process at the Algiers Water Purification Plant is similar to that of the Carrollton Water Plant, utilizing the same water treatment chemicals with a slightly modified application scheme for their upflow clarifiers.

The Carrollton plant normally yields about 115 million gallons per day of finished water for the east bank of Orleans Parish. The Algiers Plant, which serves the predominantly residential west bank portion of the parish, purifies about 10 million gallons per day of water. Combined, the two plants treat approximately 47 billion gallons of water per year, removing 20,000 tons of solid material from the raw river water.

The treated water at the two plants is pumped through more than 1,610 miles of mains to more than 160,000 service connections. It is delivered to approximately 440,000 people on the east bank of Orleans Parish and approximately 57,000 people on the west bank.