Frequently Asked Questions

Yes! Taste and odor is a palatability issue. The palatability change that results from a naturally occurring algal bloom does not alter the quality of the water provided to the cities and the communities served. The water supply remains safe for use with no health risks created by these events.

Overview

A natural occurrence in all surface water supplies, an "algal bloom" is responsible for the taste and odor changes in the treated drinking water supply. Algal blooms usually occur in Lavon Lake in late July and into August each year but can occur at any time if the right conditions exist in the water supply reservoir.

Summer Algal Blooms

As hot temperatures remain prevalent, ideal conditions are set for an "algal bloom." Summer algal blooms occur when high temperatures warm the reservoirs, little or no rainfall has occurred, and sunlight penetrates the water allowing photosynthesis to occur. When these conditions are present, the blue-green algae species Nostoc and Anabaena will reproduce or "bloom" giving the water an "earthy" or "musty" taste.

Winter Algal Blooms

The mid-summer "algal bloom" is the most common; however, infrequently a winter algal bloom can create taste and odor changes in the water supply during cooler weather patterns. When winter algal blooms occur, an earthy or metallic taste and/or odor might be noticeable in the water supply.

Annual Temporary Change in Disinfectant

(also known as chlorine maintenance)

Each spring for one month, NTMWD temporarily suspends the use of ammonia and uses free chlorine as the secondary disinfectant to maintain water quality year-round. Some people may notice a stronger smell or taste of chlorine during this time. While chlorine levels are consistent with the rest of the year, the temporary suspension of ammonia can make the smell or taste more noticeable. The water remains safe to drink and use. Learn more about the temporary change in disinfectant.

Currently, NTMWD laboratory personnel perform algal counts to confirm the occurrence of an algal bloom and the algal species that are responsible for the changes in taste and odor. We can reduce, but not eliminate, the taste and odor issues using current water treatment processes.

The NTMWD has implemented the use of ozone disinfection, which is expected to significantly reduce and/or eliminate taste and odor issues caused by algal blooms. Previous studies and thorough testing have shown that the use of ozone, an oxidation process, to supplement the current treatment process can provide additional advantages including:

• micro-flocculation to reduce chemical usage
• micro-constituent oxidation, and taste and odor control

While no taste and odor control process is 100% effective, ozonation greatly eliminates or minimizes the palatability issue of the water supply. Our consultants will continue to analyze the potential causes of taste and odor episodes and additional methods to address the issue.

Nutrients must be present - such as nitrogen, phosphorus, and calcium, which are derived from decaying vegetation in the lake.

Turbidity has lessened - the turbidity or cloudiness of the lake water has cleared up, allowing the penetration of the sunlight. This occurs due to lack of rainfall.

Temperature increase - the optimum temperature range of the lake water for an algal bloom to occur is between 80° - 85°. This is provided through many hot summer days.

When all conditions are met, photosynthesis will take place and the algae will grow and/or proliferate. Algal species, such as anabaena, secrete an "oily" substance from their cells that causes an odor in the water supply. Aquatic fungi, actinomycetes, grow on dead and decaying algae and cause an earthy taste in the water.

Individuals sensitive to taste and odor differences in the water related to the algal blooms and/or our annual temporary change in disinfectant might try the following:

Drinking Water

• Add a slice of citrus or cucumber
• Refrigerate water in an open pitcher
• Run the tap for a bit before using

Bath or Shower

• Add a crushed 1000mg vitamin C tablet to bath water

Download more tips to reduce taste and odor. (PDF)

While rashes in general are very common, they have not been directly linked to drinking water treated with chlorine. For sensitive individuals, a Vitamin C tablet added to bath water can minimize the chlorine. You can also consider installing filters on faucets and showers. According to medical toxicologist Scott Phillips, MD, "There have been no scientific studies suggesting an association between psoriasis and chlorine. If you are experiencing a rash that you are concerned about, you should discuss the matter with your dermatologist." See more health-related questions and answers (PDF) from Dr. Phillips.

Since chloramines are not as reactive as chlorine with organic material in water, they produce substantially lower concentrations of disinfection by-products (DBPs) in distribution systems. Some disinfection by-products, such as trihalomethanes (THMs), may have adverse health effects at prolonged high levels. The EPA closely regulates these disinfection byproducts, and the results of monthly tests indicate that NTMWD water contains low amounts of DBPs that are well within the range that is considered safe by the EPA.

The Water Research Foundation, the nation's leading water research group, recognizes that periodic chlorine maintenance is a preventive measure to reduce the potential for nitrification (process by which ammonia is changed into nitrates by bacteria) which can occur in water distribution systems during warmer months. View the Chlorine Maintenance video.