The water crisis in Flint, Michigan had once again highlighted the fact that water distribution systems, including the portion within individual buildings (which are generally the responsibility of property owners), are not inert. In the US, water utilities are obliged to produce water that is acceptable for drinking (and other uses) at the consumers taps.
Without getting into the politics, as someone who has done a lot of work in water treatment, and water chemistry, I have a number of questions:
- A basic measure of the stability of water is the corrosion (or stability) index. I have not seen basic data on the raw water basic chemistry of the Flint River, nor the chemistry of the major species (alkalinity, hardness, pH, sulfate, chlorides) after treatment. General Motors apparently went off the Flint Water supply due to high chloride levels (http://www.freep.com/story/news/local/michigan/2015/10/10/missed-opportunities-flint-water-crisis/73688428/). For quite some time, the concept of stability indices (Langelier, Ryznar, Larson Ratio, etc) have been well known as tools to assess the aggressiveness (corrosivity) of a water. For example, see this paper from 1980 (Millette, James R., Arthur F. Hammonds, Michael F. Pansing, Edward C. Hansen, and Patrick J. Clark. 1980. “Aggressive Water: Assessing the Extent of the Problem”. Journal (american Water Works Association) 72 (5). American Water Works Association: 262–66. http://www.jstor.org/stable/41270478.) There is no single universal tool as pointed out by Marc Edwards in his important review in 2001(McNeill, Laurie S., and Marc Edwards. 2001. “Iron Pipe Corrosion in Distribution Systems.” Journal of the American Water Works Association 93 (7):88-100.)
- It seems clear now that as early as March 2015, a consultants report was issued in which the addition of corrosion control chemicals was advised (http://www.freep.com/story/news/local/michigan/flint-water-crisis/2016/01/21/flint-red-flag-2015-report-urged-corrosion-control/79119240/).
The full report from Veolia is online and has a suite of important and prioritized recommendations to take. The response of this in terms of decisions to take or not to take action will be interesting to watch. However the focus of this report was NOT corrosion control, as exemplified in this quote:
“The primary focus of this study was to assure compliance with the TTHM limits. That is not the only problem facing the city and its customers though. Many people are frustrated and naturally concerned by the discoloration of the water with what primarily appears to be iron from the old unlined cast iron pipes. “
- In the absence of corrosion control, one would expect that the solubilization of iron would cause a decrease in the chlorine residual. Rhodes Trussell reviews the important relationships between corrosion, residual, and disinfection byproduct formation (http://www.awwa.org/publications/journal-awwa/abstract/articleid/13992/issueid/33528176.aspx?getfile=/documents/dcdfiles/13992/waternet.0049164.pdf). Either no action was taken if the chlorine residual sampled in the distribution system was noticed to drop from previous levels, or the chlorine dose was boosted, and potentially resulted in increased disinfection byproduct formation. Given that Flint had apparent concerns about compliance with TTHM levels, they may have been reluctant to increase residual. It would be interesting to see lab data sheets for chlorine residual measurements in the distribution system before and after the switchover to Flint River water.
- If the chlorine residual dropped, then microbial levels in the distribution system could have increased. Some, but not many, utilities measure heterotrophic plate count bacteria (HPC) in the distribution system. I would expect their levels to have increased with a drop in residual.
- While the connection between the elevation of the Legionella case count subsequent to the switchover is possible, a direct connection may never be known because of the absence of samples from many of the clinical cases. Frequently a genetic match between clinical isolates and environmental isolates is deemed necessary to make a definitive connection.
I will post subsequent thoughts and comments as they develop.