Countywide boil-water advisory in effect through Monday (Sept. 21) after turbidity spike at Bloomington water plant

All Monroe County residents are being advised to boil water used for drinking, cooking and oral hygiene for at least two minutes. That’s after City of Bloomington Utilities (CBU) recorded turbidity at the Monroe water treatment plant above the maximum allowed level.

The precautionary boil-water advisory is scheduled to remain in effect until 3 p.m. Monday, Sept. 21, unless CBU issues different instructions before then.

If water coming from a faucet is cloudy, CBU says residents should first run cold water from a sink or tub until the water runs clear. Water used for drinking, cooking or oral hygiene should then be boiled for at least two minutes before using it. Boiling is not necessary for bathing, laundry or other household uses, according to CBU.

Turbidity is essentially a measurement of cloudiness. It can be caused by very small particles of clay, silt, organic material, microorganisms or material associated with the treatment process itself.

In connection with a boil water news release issued two years ago, CBU said that high turbidity itself has no health effects, but turbidity can interfere with disinfection, and provide a medium for microbial growth.

The news release about the current boil water order was issued around midnight on Sept. 20.

According to the news release, residents with questions can call CBU at 812-339-1444 or email wq@bloomington.in.gov or check the CBU website. CBU says it will issue another announcement when the advisory is lifted.

During a turbidity incident in 2024 incident, CBU gave an explanation why the alert applied to all of Monroe County, rather than just customers billed directly by CBU. It’s because Bloomington supplies water to other utilities in the county as wholesale customers.

Power outages, low tank level cited

According to CBU, the elevated turbidity followed overnight storm-related power outages that caused lower-than-normal water production at the Monroe water treatment plant. The reduced production in turn caused a low water level in the plant’s primary storage tank, which CBU says “contributed to” the elevated turbidity.

CBU says its staff increased water-quality monitoring and adjusted plant operations to stabilize production and turbidity. The release says staff are continuing to monitor turbidity and other water-quality indicators as the system returns to normal operating conditions.

The news release does not say how high the turbidity actually got. CBU reports only that routine monitoring found a level above the 1.0-unit maximum cited in the release. It does not give the peak reading, the time when the threshold was crossed, how long the elevated readings persisted, or what the most recent reading was when the announcement was issued.

The release also does not say what testing or other conditions that CBU and the Indiana Department of Environmental Management will require before Monday’s advisory can be lifted.

The release does not provide detail about the power failure, like its duration, what plant equipment lost power, whether backup power was available or how low the levels in the primary storage tank got.

CBU’s public data set for electricity usage at the Monroe water treatment plant production appears to be updated monthly, which means it goes only through Aug. 31. When the September data is uploaded, it should be possible to see exactly how production at the plant was affected in the time leading up to the Sept. 20 advisory.

Technical details on turbidity

The turbidity measurement is generally expressed in NTUs (nephelometric turbidity units). A nephelometric measurement works by shining light through a water sample and measuring how much of that light is scattered by particles in the water. Higher scattering produces a higher turbidity reading.

So turbidity measures an optical property of the water. It does say what the particles are. A turbidity reading by itself does not establish whether bacteria, viruses or parasites are present. EPA describes turbidity as an important indicator of treatment performance. That’s because an increase in filtered-water turbidity can signal that particles are getting through the filtration process.

For water systems using conventional or direct filtration, federal drinking-water rules require turbidity to be 0.3 NTU or lower in at least 95% of measurements during a month, with no measurement allowed to exceed 1 NTU.

Similar countywide advisory in 2024

The current situation resembles a countywide boil-water advisory issued a little more than two years ago, on Aug. 17, 2024, when CBU also reported a turbidity measurement above the 1-NTU limit.

The cause described at the time was different. In the 2024 incident, CBU said water containing sand from the plant’s filtration system had moved forward into a later stage of treatment during a filter-backwashing operation. That advisory was ultimately lifted on the morning of Aug. 19.