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Geosmin - Frequently Asked Questions

What is causing the taste and odor experienced by some customers served by the Fort Worth water supply?

Because Tarrant Regional water district is performing required and scheduled construction maintenance on the pipeline from Richland-Chambers Reservoir, on Jan. 6, Fort Worth’s Rolling Hills Water Treatment Plant and Westside Water Treatment plants were switched to using Lake Benbrook as the sole source water. Test results from Tarrant Regional Water District over recent weeks are showing an increase in the geosmin levels in Lake Benbrook. Geosmin, even at low levels, can be detected by the average person.

What is geosmin?

Geosmin is a naturally occurring compound produced by bacteria in soil and algae found in surface water. Cold temperatures kill off algae in surface water, and the dead algae release the geosmin. 

Where is the odor and taste occurring?

There are reports of an earthy, musty-type odor/taste in the water coming from customers throughout Arlington and mostly from customers in south, central and east Fort Worth, as well as the other entities that purchase and resell treated water from Fort Worth.

Is the water quality affected?

While the taste and odor can be unpleasant, geosmin is not toxic or harmful. The water remains safe to drink. On-going testing continues to show an absence of harmful bacteria and other pathogens in the water.

How long will the taste and odor last?

It is impossible to predict the onset of an incidence of geosmin, or how long it will last. Geosmin compounds have been detected in TRWD lakes remain in lakes throughout the year at varying levels. The highest levels are typically detected in January and February.

Tarrant Regional Water District regularly tests the water supply sources for various water quality parameters. , the geosmin level in Lake Benbrook rose from 91.3 nanograms per liter (or parts per trillion) in mid-November to more than 1,000 nanograms per liter on Jan. 23. 

To put this in context, the general threshold for human detection is about 50 nanograms per liter; however, people with sensitive pallets can detect geosmin in drinking water at concentrations as low as 5 nanograms per liter. This is why some customers notice the taste and odor while others do not.

Since Jan. 23, the Lake Benbrook water has been blended with the Cedar Creek Lake water to reduce the geosmin levels in the water entering tha plant. Cedar Crekk has historically had very low geosmin levels.

Can the taste and odor be reduced at the tap? 

To make the water taste better, try chilling it, adding ice cubes, a slice of lemon, or a few drops of lemon juice.

What does it smell like?

Geosmin typically produces an earthy or musty odor as is found in the odor of overturned rich soils, and is present in some foods such as beets, spinach, and mushrooms.

Why do we smell it? 

The human nose is extremely sensitive to geosmin. If you poured a teaspoon of geosmin into the equivalent of 200 Olympic-sized swimming pools, you would still be able to smell it.

The general threshold for human detection is about 15 ng/l (15 nanograms per liter = 15 parts per trillion). However people with sensitive pallets can detect these compounds in drinking water when the concentration is as low as 5 ng/l.

Heating the water increases the volatility of these compounds, which explains why the smell is more easily detected when you are in the shower or when used for hot beverages.

Can it be removed from the drinking water? 

Geosmin cannot be removed by conventional water treatment processes, but ozone disinfection, which is used in all Fort Worth water treatment plants, can be effective. Both water utilities have increased the dosage of ozone at the treatment plants to try to resolve the taste and odor problem. There is a point at which geosmin levels get so high that even ozone treatment is ineffective.

Does geosmin occur elsewhere? 

Geosmin is common in many jurisdictions across the United States, Canada and elsewhere in the world. It is found in all of Tarrant Regional Water District’s supply sources, but Lake Benbrook historically has seen the highest levels.