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Water Taste and Odor Concerns Update

Update On Taste and Odor Concerns In Drinking Water 
(May 14, 2013)

Based on analyses on samples taken at the treatment plants and the decrease in calls from customers, the strategies implemented have addressed the taste and odor concerns.  Now that the issue has been abated, Water Management will begin flushing the system. Further updates will be provided.

Tap water remains safe to drink
Typically the City of Durham’s tap water has a pleasant taste and is odor free. Currently many customers are experiencing taste and odor in their tap water. This taste and odor has been traced to an increased presence of specific odor/taste causing algae species in the City’s source water supply. While algae are a natural and essential part of a reservoir’s ecosystem, under certain conditions some algae can reproduce to levels that cause various nuisance effects in lakes, streams, and other water bodies.  These nuisance effects include excessive accumulations of foam, scum, discoloration of the water, and taste and odor problems in these water bodies. At this time, both of Durham’s water sources - Lake Michie and Little River – have excess levels of the algae populations that create taste and odor issues*.
In addition to the Division of Water Supply and Treatment’s usual treatment processes, water treatment plant personnel at the Williams Water Treatment Plant (WTP) are adding potassium permanganate into the raw water at the head of the treatment process. Staff is also adding sodium permanganate to the raw water as it enters the terminal reservoirs at each of the WTPs. These chemicals are widely used in the water treatment industry for taste and odor control.  Additionally, the treatment staff has begun to feed a drinking water approved formulation of copper sulfate to the raw water entering the terminal reservoirs at each treatment facility to suppress the algae growth. Once the taste and odor levels are back to normal, the department will aggressively flush the system to deliver the better tasting and odor free water to all our customers as quickly as possible. Because both of the supply lakes are affected, it will take longer than initially anticipated to resolve this issue. We appreciate your patience and understanding and the department shall continue to work diligently to address this taste and odor event as proactively as possible. Please remember, despite the unpleasant taste and odor, your drinking water remains safe to drink and remains in full compliance with all state and federal drinking water standards.
*Based on preliminary results of samples collected Friday, May 3
What are algae?
The term "algae" generally refers to a wide variety of different and dissimilar photosynthetic organisms that are usually only visible using a microscope. Depending on the species, algae can inhabit fresh or salt water. Fresh-water algae, also called phytoplankton, vary in shape and color, and are found in a large range of habitats, such as ponds, lakes, reservoirs, and streams. They are a natural and essential part of the ecosystem. In these habitats, the phytoplankton are the base of the aquatic food chain. Small fresh-water crustaceans and other small animals consume the phytoplankton and in turn are consumed by larger animals. Under certain conditions, several species of true algae as well as cyanobacteria may cause various nuisance effects in fresh water, such as excessive accumulations of foams, scums, and discoloration of the water. When the numbers of algae in a lake or a river increase explosively, an algal "bloom" is the result. Lakes, ponds, and slow-moving rivers are most susceptible to blooms.
Algal blooms are natural occurrences, and may occur with regularity (e.g., every summer), depending on weather and water conditions. The likelihood of a bloom depends on local conditions and characteristics of the particular body of water. Blooms generally occur where there are high levels of nutrients present, together with the occurrence of warm, sunny, calm conditions. Aquatic ecologists are concerned with blooms (very high cell densities) of algae in reservoirs, lakes, and streams because their occurrence can have ecological, aesthetic, and human health impacts. In water bodies used for water supply, algal blooms can cause physical problems (e.g., clogging screens or filters) or can cause taste and odor problems in waters used for drinking.  [Excerpt from]