Algae in Drinking Water Supplies

Tap Water Remains Safe To Drink

Durham’s water is safe to drink and use for all drinking water purposes. The Department of Water Management staff routinely tests our water sources – Lake Michie and Little River Reservoir – to look for any excess growth of algae. Our tests of Durham’s water supply show that the toxin-causing algae creating concerns for the City of Toledo, Ohio, are well below levels that are considered unsafe.

About Algae

Algae are a natural and important part of a reservoir’s ecosystem. However, under certain conditions some algae can reproduce to levels that cause changes in fresh water. These changes do not affect the safety of our drinking water but can include excessive buildups of foam and scum, a change in the color of the water and taste and odor problems. Although the city’s source waters experienced a slight increase in algae species that cause odor/taste changes, staff quickly addressed the issue. The water returned to normal with the addition of potassium permanganate and copper sulfate. These chemicals are widely used in the water treatment industry for taste and odor control.

The term algae refers to a wide variety of different organisms that use light to grow. Depending on the species, algae can live in fresh or salt water. Freshwater algae, also called phytoplankton, vary in shape and color. They are found in a large range of habitats, such as ponds, lakes, reservoirs, and streams. Algae are the base of the aquatic food chain in these habitats. Small aquatic animals eat the phytoplankton and are then eaten by larger animals.

Algal Bloom

Under certain conditions, several species of true algae as well as cyanobacteria may cause excess foam, scums, and discoloration of the water. Algal blooms occur when the numbers of algae in a lake or a river increase explosively. Lakes, ponds, and slow-moving rivers are most prone to blooms. Algal blooms are natural, and may occur regularly (e.g., every summer). This will depend 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 during warm, sunny, calm conditions in water where nutrient levels are high. Aquatic ecologists are concerned with blooms of algae in reservoirs, lakes, and streams because they can have ecological, aesthetic, and human health impacts. In waterbodies used for water supply, algal blooms can cause physical problems (e.g., clogging screens or filters) or can cause taste and odor problems.