Managing Water Quality

Treatment Processes

Untreated (raw) water is transmitted from Carter Lake to the Carter Lake Filter Plants for treatment. Certified plant operators manage the treatment process, evaluating water quality throughout treatment. Water moves through the treatment plant in five stages:

Coagulation Flocculation

Raw water from Carter Lake and on occasion from Dry Creek Reservoir flows into our treatment plants where coagulants, polymers, and chlorine Dioxide are added. This process causes small particles to stick to one another, forming larger particles.


The water is then filtered through, depending on the treatment plant, membranes or fine layers of filter media.


Following filtration, chlorine is added to the water as a protection against viruses, bacteria, and other micro-organisms that might remain. The amount of chlorine added is carefully monitored, and the residual levels of chlorine are continuously monitored throughout the facilities.


Fluoride occurs naturally in source water and fluoride is added to the treated water to meet the recommended health levels.

Corrosion Control

pH is maintained by adding soda ash and/or sodium hydroxide. A corrosion inhibitor to reduce the corrosiveness of drinking water is added.

Managing Treated Water Quality in the Distribution System

Once water is "finished" or treated, it is conveyed to LTWD’s distribution system. LTWD conducts additional water quality tests at locations throughout the distribution system, including water taps in customer homes and businesses.

Annual system flushing also helps ensure water quality by reducing sediment in the system’s pipes. In the spring, fire hydrants are opened, allowing water at high pressure to flush the pipes.

In addition to managing the distribution system to maintain quality, customers may have questions about common concerns or issues:

  • Dirty Water
  • Disinfection Byproducts
  • Fluoride
  • Lead
  • Trace Pharmaceuticals
  • Water Hardness

Dirty Water

Occasionally, "dirty" or discolored water may appear when the faucet is turned on at your home or work. Discolored water usually originates in the water distribution system or your home's or business's private plumbing systems. Corrosion or rusting of the interior surfaces of metal pipes is a primary source of discoloration and particles that can appear in your water. Water main breaks, fire hydrant breaks and system flushing may cause discolored or dirty water to appear temporarily. Your home's plumbing, including the hot water heater, may also be a source of discolored water. Please call our office for assistance if you discover dirty or discolored water at the tap.

Taste and Odor

Typically, LTWD’s water is both tasteless and odorless or has minimally perceived taste and odor. However, water can acquire taste and odor qualities from our source water streams and reservoirs, in the treatment process and in the distribution system. Learn more about taste and odor in water on our FAQs page, email us, or call our office with your questions or concerns.

Disinfection Byproducts

Water Disinfection is a necessary part of the water treatment process. It kills pathogens, and it produces chemical byproducts. Disinfection is typically done by adding small amounts of a chlorine-based disinfectant to water. It destroys water-borne microbes, bacteria, and viruses — organisms that can cause serious illnesses or death. Because there is a possibility that microorganisms might get into treated water after it leaves the treatment plant, public health regulations require that tiny but detectable amounts of disinfectant must remain in the water all the way to the tap. Small amounts of disinfectant are added to the water before it leaves the plant, and the disinfectant reacts with organic substances in the water, byproducts are created.

The Environmental Protection Agency regulates the quality of drinking water on a federal level. Its regulations cover acceptable, safe levels of microorganisms, disinfectant, and disinfection byproducts.


Fluoride is a naturally occurring compound in the District’s source water. It enters the water when fluoride-rich minerals in soils and rock dissolve. During the treatment process, fluoride is added to the water to meet the State’s recommended level of 0.7 milligrams per liter. Fluoride is added to the water to help promote dental health and prevent tooth decay.


Lead is a naturally occurring metal that is all around us. It was used for many years in paints, plumbing and other products found in and around homes. The Environmental Protection Agency has determined that lead can cause health problems if it accumulates in a person’s body over time. High levels of lead in your household drinking water can have significant health impacts, especially for children and pregnant women.

Trace Pharmaceuticals

Trace pharmaceuticals are sometimes called microconstituents or emerging contaminants. They are products that enter the water supply through agricultural runoff or from human sources. A high percentage of pharmaceuticals in wastewater enter the water supply when people dispose of medicines in the sink or toilet. Most, if not all, pharmaceutical products — whether used in animals or in humans — are used in doses at which some amounts are passed through the user and back into water systems. Today’s technology allows detection of more substances at lower levels than ever before. As analytical methods improve, pharmaceutical compounds and personal care products are being found at very low levels in many of our nation's lakes, rivers and streams. All trace pharmaceuticals currently are not monitored by LTWD, although monitoring may occur in the future.

Water Hardness

Hardness in water is defined as the sum of the calcium and magnesium concentrations (salts), expressed as calcium carbonate. The hardness of the water varies with the amounts of these salts. They originate when subterranean and surface waters absorb minerals, including compounds of calcium and magnesium carbonates, bicarbonates, sulfates and chlorides – giving water its hardness. Hard or soft water are not health concerns, but may result in a mineral taste (hard) or a flat, unpleasant taste (soft).

General guidelines for classification of waters are: 0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard.

The average total hardness of LTWD’s finished water is approximately 32.00 mg/L. (Value from 2022)