Seasonal Algae Blooms Causing Water Taste and Odor Issues

Water consumers across Harris County are once again complaining of odor and foul tasting water.

The North Harris County Regional Water Authority (NHCRWA), one of the largest wholesale drinking water suppliers for independent neighborhoods, municipal utility districts, small municipalities, and permitted well owners released a statement saying “Some customers have reported taste and odor issues with the water being delivered by the North Harris County Regional Water Authority. This water, purchased from the City of Houston, is withdrawn from Lake Houston and is treated at the City’s Northeast Water Purification Plant before being delivered to the Authority.”

The taste and odor issues are the result of naturally-occurring compounds sometimes produced by seasonal algae blooms.

The NHCRWA has deliberately managed their system, reducing the amount of water taken from the City of Houston and supplementing the water supply by using NHCRWA wells.

NHCRWA says “The water being delivered is perfectly safe to drink.”

The Questions & Answers below are provided by the City of Houston Department of Public Works and Engineering Public Utilities Division in reference to recent changes detected in Lake Houston.

What is in the water that has caused the recent change in taste or odor?

We have detected increased levels of geosmin and MIB in our untreated surface water in Lake Houston and these substances are known to produce earthy or musty taste or odor in drinking water. Geosmin and MIB (2-methyl isoborneol) are naturally-occurring compounds sometimes produced by seasonal algae blooms. The substances are detectable by the human nose even at very low concentrations. This is similar to the taste and odor event Houston experienced in June. However, it is different than the event that recently occurred in Ohio. The water is safe to drink.

According to the Water Research Foundation, “There are hundreds of types of algae, but only a few produce chemicals that make water taste or smell unpleasant. When algae die, they release compounds. Two of the more troublesome byproducts are MIB and geosmin. Both produce an earthy/musty taste. MIB mimics the smell of fresh dirt; geosmin is the compound that gives beets an earthy odor. Neither is harmful to people.” (AWWA Water Research Foundation, 2006)

What is the City of Houston doing to remedy the issue?

Since MIB and geosmin are naturally-occurring, they will naturally diminish in the upstream water supply with time and weather changes.

How are you monitoring the situation?

We are taking additional water samples to better understand and track the levels of these substances, as well as maintaining our standard program of sampling and testing to assure that our drinking water is safe. We are monitoring Lake Houston and there have been no observed nor reported fish and/or waterfowl “kills” which are indicators of a toxic algae bloom. Furthermore, there is no history of algal toxins in our water supply.

What if it does not naturally clear from the system?

Conventional water treatment is ineffective for removal of geosmin and MIB. Treatments such as powdered activated carbon (PAC), ozonation and biofiltration have been effective for removal of these compounds. The City of Houston system does have a PAC system at the water plant treating Lake Houston water but it has not been effective at fully mitigating this event. We are reviewing the potential use of portable and temporary systems should this become necessary.

What can I do at home?

According to the Water Research Foundation, water is safe to drink when MIB and geosmin are present, but it may be unappealing when there are taste and odor problems. You can improve the taste and odor by refrigerating a pitcher of tap water. Additionally, standard home water filtration systems that contain carbon should mitigate the taste and odor of these substances.

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