AUSTIN (KXAN) — After Austin Water announced a citywide boil water notice late Saturday, city officials stressed there was no indication of contamination in Austin’s water supply. But what leads to issuing a boil water notice in the first place?

What leads to a boil water notice?

In this latest example in Austin, the citywide notice was due to high turbidity, or cloudiness, in the city’s water system. High turbidity is one of two key violations outlined by the Texas Commission on Environmental Quality that lead to boil water notices. This is due to the potential risk of an “acute health threat” if customers consume water containing excessive E. coli levels or that has high turbidity.

If a public water system detects a heightened concentration of E. coli that exceeds the maximum contaminant levels permitted, that system must issue a boil water notice. With turbidity, TCEQ requires the issuance of a boil water notice if high turbidity levels are detected, due to indications of a “severe failure in filtration and possibly other treatment processes at the plant.”

A TCEQ spokesperson said public water systems are required to maintain a combined filter level below 0.3 Nephelometric Turbidity Units, or NTUs, 95% of the time. If the combined filter level of a public water system exceeds 5.0 NTUs, the system operator is required to issue a notice; on Saturday, Austin Water filter levels exceeded that 5.0 NTU threshold.

While both E. coli presence and high turbidity are the two explicit violations that lead to an issued boil water notice, other events that could lead to compromised water sources and result in a notice include:

  • Low water pressure (below 20 pounds per square inch)
  • Water outages
  • Storage, well problems
  • Mechanical equipment problems
  • Power outages
  • Natural disasters
  • Treatment facility issues

Austin residents will remember the two other times the city has issued a citywide boil water notice: once in October 2018 and again last February amid the winter storm.

In 2018, severe flooding resulted in excess sediment in water supplies, increasing turbidity and leading to a notice. Last year’s storm caused a combination of both low water pressure and power outages at city treatment facilities, resulting in a notice.

What’s the risk of drinking tap water during a boil water notice?

Turbidity is used as a metric to determine filtration effectiveness, according to the U.S. Environmental Protection Agency. On Sunday, Austin Water Director Greg Meszaros noted a spike in turbidity went undetected until Saturday morning, with city leaders attributing the error to operating staff.

When turbidity levels are higher, that can lead to potentially higher levels of bacteria in water sources. If consumed, those bacteria can cause gastrointestinal symptoms like nausea, cramping and diarrhea.

Still, officials said this notice was a precautionary measure taken, as required by TCEQ.

“We have no indication that there was a contamination,” Meszaros said Saturday night.

While no contaminants were detected, boiling water used for consumption is still recommended to prevent any physical side effects. For children, pregnant people, older adults and those with compromised immune systems, waterborne bacteria or illnesses might impact them more severely than those without immunodeficiencies.

Austin Water customers are recommended to bring their water to a rolling boil and maintain that for two minutes, allowing it to then cool before consuming.

What’s the timeline for issuing a boil water notice?

Under TCEQ requirements, public water systems like Austin Water have 24 hours after first detecting a violation to issue a notice. City officials said Sunday operating staff first noticed higher turbidity levels around 8 a.m. Saturday; the citywide notice was officially issued around 7:30 p.m. that same day.

Austin Water outlined a five-step system before a boil water notice is officially lifted:

  1. Ullrich Water Treatment Plant back online — officials said the plant went back online Sunday
  2. Ullrich is operating at normal production levels — officials said the plant’ production levels resumed as normal Sunday
  3. Water sampling begins Monday — officials said they began this step Monday evening. AW got approval from the state to begin the water sampling process at 5:45 p.m.
  4. Water sampling results show no water quality issues (tests results take 24 hours to process and receive)
  5. TCEQ authorizes lifting the notice

As of Monday, city officials continue to target lifting the notice by end of day Tuesday.