Effectiveness of Prevailing Flush Guidelines to Prevent Exposure to Lead in Tap Water

Flushing tap water is promoted as a low cost approach to reducing water lead exposures. This study evaluated lead reduction when prevailing flush guidelines (30 s–2 min) are implemented in a city compliant with lead-associated water regulations (New Orleans, LA, USA). Water samples (n = 1497) collected from a convenience sample of 376 residential sites (2015–2017) were analyzed for lead. Samples were collected at (1) first draw (n = 375) and after incremental flushes of (2) 30–45 s (n = 375); (3) 2.5–3 min (n = 373), and (4) 5.5–6 min (n = 218). There was a small but significant increase in water lead after the 30 s flush (vs. first draw lead). There was no significant lead reduction until the 6 min flush (p < 0.05); but of these samples, 52% still had detectable lead (≥1 ppb). Older homes (pre-1950) and low occupancy sites had significantly higher water lead (p < 0.05). Each sample type had health-based standard exceedances in over 50% of sites sampled (max: 58 ppb). While flushing may be an effective short-term approach to remediate high lead, prevailing flush recommendations are an inconsistently effective exposure prevention measure that may inadvertently increase exposures. Public health messages should be modified to ensure appropriate application of flushing, while acknowledging its short-comings and practical limitations.


Information about New Orleans Sewerage and Water Board Water Treatment System:
The New Orleans Sewerage and Water Board (S&WB) operates two water treatment plants-one on the East Bank and the other on the West Bank of New Orleans (NOLA). This study focused on homes served only by the S&WB's East Bank or Carrolton plant. The Carrolton plant provides an average of 135 million gallons of water per day to an estimated population of 286,603 (S&WB 2016). The plant uses a conventional treatment system to purify water from the Mississippi River. Ferric sulfate and polyelectrolyte is used for coagulation followed by flocculation and sedimentation. Chlorine, in the form of sodium hypochlorite, is used as the primary disinfectant and chloramines are used as the secondary disinfectant. Lime is used for corrosion control pH adjustment and sodium hexametaphosphate is added as a sequestrant. The final step are fluoridations followed by filtration through rapid gravity filters (sand and anthracite) (Black and Veatch 2016). The city's water quality parameters are presented in Table S1, Supplementary Materials. Source: NOLA S&WB. Samples collected 1-1-2015 to 12-31-2015 from 11 points of entry to distribution system.

The New Orleans Sewerage and Water Board's Consumer Confidence Report Prior to Study Commencement (2015):
After EPA regulations on flush time recommendations were relaxed, the city's water utility, the Sewerage and Water Board, continued to promote the original flush recommendations from 2009 to 2015 [41,46]. At the commencement of this study, the utility encouraged residents to flush their taps "for 30 seconds to 2 minutes before using water for drinking or cooking" daily under normal use conditions [41] ( Figure S1, Supplementary Materials). Figure S1.

New Orleans, LA Study Participant Premise Plumbing and Service Line Lengths:
To determine the most probable location in the water distribution system or premise plumbing that each sample type may have been sitting during the stagnation period, an estimate of the volume of water and flush times required to purge the lines was derived based on estimated flow rates at low flow (3.0 liters per minute) and high flow (8.3 liters per minute); typical premise and service line pipe diameters; and survey respondent measurements of service lines and premise plumbing ( Figure S2, Supplementary Materials).
A 250-mL sample is estimated to represent water in approximately 2.4 meters (or 8 feet) of piping. Figure S2. Percent of survey respondents by reported length of premise plumbing + service line measurements (meters)(n=80) The lengths of water service lines and premise plumbing pipes were estimated based on resident measurements reported on returned surveys ( Figure S2, Supplementary Materials). Residents were asked to measure the distance from the middle of the street to the water line as it enters the home (service line length) and the distance from where line enters home to the kitchen tap as measured along wall (premise plumbing). Researchers also derived google map measurements of potential service line lengths for all sites, based on measures taken from the center of the street to the front of the home in the satellite view of Google Maps using the distance and area tool.

Difference in Water Lead Levels in Flushed and First Draw Hot Samples Compared to First Draw Cold Water Samples:
The results of the WLL differences from FD to flushed samples (Table 2, Figure S3) demonstrate a small but significant increase (median=0 ppb and mean=0.6 ppb, p=0.04) in WLLs from FD to F30S sample. No significant change in WLLs was observed from FD to F3M samples (p=0.219). Small but significant declines in WLLs was observed in F6M (median=0 ppb and mean= -0.2 ppb) and FDH (median= -0.1 ppb and mean= -0.4 ppb) samples, compared to FD samples (Table 2; Figure S3, Supplementary Materials). Figure S3. Distributions of the difference in water lead levels (WLLs) in cold water samples collected at first draw (FD) compared to WLLs in samples collected after various flush times Key: FDH: first draw hot water; F30S: 30 second flush; F3M: 2.5-3 minute flush; and F6M: 5.5-6 minute flush samples. Diamonds inside box: mean value; line inside box: median value; bottom and top edges of box: 25th and 75th percentile; lower fence: 1.5 IQR (interquartile range) below 25th percentile; upper fence: 1.5 IQR above 75th percentile. Notes: Measures outside the range of -3 and 3 ppb were not shown. Refer to Table 2 for the minimum and maximum values.

Water Lead Levels And Flushing Efficacy Associated With Atypical Use Conditions
While not a planned part of the study, conditions arose which allowed us to evaluate the impact of a onetime 15-minute utility flush on WLLs after lead service lines replacements at five residential sites. Lead service line replacements and construction are known to increase lead in water due to construction disturbances and galvanic corrosion for periods of weeks to years [19,30,38]. Five of our study participants contacted the city's water utility after our testing to request removal of their lead service lines. All but one of these residents received a partial lead service lines replacement (i.e., only the utility or customer side was replaced); while one had the full lead service lines replaced (from water main in the street to the home). All of the sites were sampled prior to, and after the line replacements and the utility or contractor 15-minute post-replacement flush. Only one of these homes was unoccupied due to ongoing home renovation work. Table S2 shows sampling procedures and WLL results for each site-unfortunately, collection procedure for the samples varied from home to home. No definitive conclusions can be drawn from the post-line replacement samples due to the small sample size and variance in the sampling procedures. However, the persistent elevation in WLLs (exceeding the EPA AL) can be seen within the week after the line replacement in occupied homes, in both the full line replacement site (6 days later) and partial line replacement Site 3 (1-2 days later). Post-line replacement WLLs reached as high as 226 ppb one day after the partial line replacement (after a post-stagnation 30 second flush).  These results suggest that rigorous extended flushing protocols may need to be repeated on a daily basis for an as yet indeterminate time period following line replacements. It is widely acknowledged that sites with partial replacements may have higher WLLs; and may require more rigorous and regular flushing than normal-use residential sites under typical conditions. [38,70]. Post-replacement flush guidelines are not always consistent, and some guidelines (i.e., one-time 15 minute high velocity flush) may not be effective for maintaining low WLLs over a long period of time. In some circumstances, utilities are not required to promote flushing, such as after voluntary lead service line replacements in Pb-compliant cities.
When lead service line replacements are conducted in cities compliant with the Lead and Copper Rule, educating consumers about flushing is only required once a year, in the utility's annual Consumer Confidence Report for utility customers [3].
New Orleans has been undergoing extensive road work, including thousands of partial lead service line replacements [48]. For homes undergoing partial lead service line replacements, New Orleans officials recommend on their Roadwork website, that residents "Run cold water at a high flow at all of your faucets for at least 5 minutes each, one at a time, starting with the faucet closest to your water meter"; clean faucets aerators; and continue to flush for at least a month before using the water [71]. At the start of this study, this information was not consistently communicated nor readily available to New Orleans residents undergoing roadwork [72]. However, the persistent elevation in WLLs we observed days after the line replacements indicates that care should be taken to flush systems rigorously and regularly after line replacements ( Table S2, Supplementary Materials).
The EPA's Science Advisory Board (SAB) stated that "the lack of mandatory water lead testing and homeowner education associated with voluntarily partial lead service line replacements suggests that in practice, voluntary replacement might be associated with greater exposure of the public to lead" [38]. The SAB recommends that utilities test the water and tell consumers to flush the lines "over a period of months" after a partial lead service line replacement; but concluded that while "line flushing appears to provide some benefit, the … time to realize the benefit (up to several weeks of flushing in the reviewed studies) likely precludes any practical implementation of this technique" [38]. Despite the general knowledge about the ineffectiveness and potential danger that partial lead service line replacements pose, they are still required by the Lead and Copper Rule when certain compliance conditions have not been met [3].
More research is needed to evaluate how frequently flushing would need to be conducted to maintain low WLLs after a partial lead service line replacement. One study simulated partial lead service line replacements in New Orleans, and observed that intermittent flushing over a two week period was not long enough to stabilize WLLs [19]. In keeping, previous studies suggest several weeks, months, or maybe years may be required to remediate increased WLL exposure after partial lead service line replacements [38,74]. These facts do not discount the benefits of more rigorous flushing protocols as an effective Pb remediation method for some systems when high WLLs are present. Improved remediation has been observed with higher velocity flushing (full open tap); continuous flushing (as opposed to intermittent flushing); increased flushing frequency and duration; and flushing at multiple taps [9, 11-12, 19, 24].
However, residents should be alerted that when conditions are severe enough to warrant more rigorous flushing protocols, as observed here after partial lead service line replacements, exposures to high WLLs are always a possibility. Flushing can mobilize particulate-bound Pb throughout the plumbing system, which can then serve as a long-term source of acute Pb exposure. Even after flushing water for 10-25 minutes, some Flint homes still had high WLLs [14]-at least one Flint tap still contained WLLs exceeding 15 ppb (217-13,200 ppb) after a 26 minute flush [75]. This was likely due to the presence of highly unstable lead scales and the continuous sloughing of particulate lead during the time in which corrosion control was not used by Flint officials. Factors associated with maintaining low WLLs under such conditions, such as flushing frequency, must be determined on a case by case basis.

Post-Study S&WB Risk Messages:
Homogenized exposure reduction and lead remediation guidelines are always susceptible to error, given the wide variability that can exist between buildings, e.g., in pipe age, lengths, materials, and diameters; scale buildup; and home occupancy and water use. Promotion of these practices need to be reconsidered as other more effective, evidence-based, low-cost technologies, such as NSF-certified faucet mount filtration devices, are now widely [82]. In acknowledgement of this issue, the US EPA's Lead and Copper Rule (LCR) Working Group recommended to US EPA officials in 2015, that the Consumer Confidence Reporting Rule be revised to exclude the currently required messaging: "When your water has been sitting for several hours, you can minimize the potential for lead exposure by flushing your tap for 30 seconds to 2 minutes before using water for drinking or cooking" [71]. Rather than promoting one-size-fits-all flush guidelines, greater effort should be expended on motivating and enabling proactive evidence-based solutions. Yet it was only after the preliminary release of our results in 2016 that S&WB revised their risk messaging and increased their flush guidelines to "30 seconds to 5 minutes"; however elsewhere in the same material, the messaging remained "30 seconds to 2 minutes"-conflicting messages which can increase confusion [84] ( Figure S4, Supplementary Material). Figure S4. The New Orleans, Louisiana Sewerage and Water Board's informational brochure: "Tips for reducing lead exposure from drinking water" (Source: NOLA S&WB's 2016 Consumer Confidence Report) The following pages present the participant survey: b. Indicate if you went through this process to find out:  Yes, I followed these steps  No 15. Any partial or full replacement of water lines outside home? A full replacement is replacement of pipes from the home to the water main in the street. A partial replacement is just replacement of pipes from the meter to the main or from the meter to the home. Thank you for participating in this study. We will contact you shortly as soon as the water test results are received, and give you guidance on next steps if needed.