What events lead up to a boil water advisory and how to avoid them.
About 1 year ago - Ron Falco, the Safe Drinking Water Program Manager, published an article on the relentless culture of health and boil advisories (March 31, 2021 article). In that article he discusses how boil advisories still occur at about the same rate even though the number of E.coli events has dramatically decreased between the year 2000 and now.
Figure 1: 25,000 people were effected by the Englewood e.coli boil advisory event (photo courtesy of “The Denver Channel”)
Since the time of the publishing of that article in March, 2021 - Colorado has seen the largest boil water advisories in recent years occur for a variety of reasons. In the next series of four short articles, we will explore several topics around boil advisories and some lessons learned in 2021 that are worth exploring. As always - the department staff are here to help water providers avoid the events that result in boil advisories as well as assist you when disaster strikes and boil advisories become necessary. The topics we will explore are as follows:
- Total coliform perfect storm - incidents that could lead to a boil advisory and how to avoid them
- Public notice to thousands - Special steps for large scale advisories
- What language do your customers communicate in? - Accomplishing public notification considering your community
- Do you really want to sample a home for compliance? - Total coliform special sample stations
Today - we will discuss the total coliform rule and how it can lead to boil water advisories. There are specific incidents to watch out for in total coliform sampling. Total coliform sampling frequency is determined by your population. While most Colorado public water systems are very small - a few systems must collect dozens or even hundreds of total coliform samples each month (see Figure 2 below). You can find your required samples in your monitoring schedule.
Figure 2: Table 11.16 from Regulation 11 (Colorado Primary Drinking Water Regulations - 5 CCR 1002-11) specifies total coliform frequency.
When a large number of samples are being collected, many things can go wrong. What many water professionals may not realize is that even if only 1 of those samples comes back positive for E.coli, then a boil advisory for the whole system could be required.
Once E.coli has been detected, if any repeat samples come back with total coliform or E.coli present, then a mandatory Tier 1 public notice is required. The difficulty of understanding the extent of the boil advisory during an E.coli positive event is that the samples take 18 to 24 hours to incubate. Once a positive sample and its repeat samples have been taken, up to 72 hours could have passed since the original sampling event.
With most water systems, it is difficult to determine the full extent of where water could circulate within 72 hours. Therefore, if a positive E.coli is detected and confirmed, the initial assumption is that the contamination may be throughout the system. Many times systems ask the question, but the contamination was only detected at one site - so why would the notice be system wide?
It is also important to remember that each total coliform sample location is a sentinel site representing your distribution system water quality. Each site does not only represent a specific location, but rather a substantial portion of the distribution system. Therefore, if there is contamination in that representative sample, contamination is presumed to be present in part or all of the distribution system pipes.
The ramification of not quickly warning the public about confirmed E.coli contamination is that a large number of people could get sick from the water because potentially impacted populations were not warned the water is unsafe to drink.
A few of the lessons learned and possible ways to avoid or minimize the impact of a boil advisory follow. However, it is important to remember that these events could happen to any public water system.
- When you take total coliform samples - it is critical that proper sampling procedures are followed. If a total coliform positive or E.coli positive occurs, follow proper sampling procedures. Inspect the site and determine if contamination exists. Ensure that sampling faucets are thoroughly disinfected before sampling and that the water is allowed to run for sufficient time to collect distribution system water.
- If the sample comes back E.coli positive - do not assume there was sampling error, or that somehow you received a ‘bad batch’ of sample vials, but rather act in a manner that the water actually contained those bacteria when you sampled and mitigate that risk.
- Focus on your distribution system and understand the fate of the drinking water - the ability to understand the hydraulics of where water can travel over time can change the fate of a boil advisory from affecting a specific area to affecting the whole system. Each water supplier must maintain redundancy in their system, balance water age, and also consider simultaneous compliance.
- Run desktop activities - do not wait for the event to occur to rehearse what the responses will be. Rather, perform ‘what if’ scenarios with staff to understand if an E.coli positive occurred in a certain area - what would be the extent of the advisory? Similar activities can be performed simulating pressure loss events.
As always, reach out to the department for guidance and partnership during challenging events. We stand ready to assist you when issues arise.
➽ Tyson Ingels, P.E Lead Drinking Water Engineer
