How safe is safe enough?

  

We don’t do very well at dealing with risk and uncertainty. Maybe because it’s so darn scary!  Risk means danger, and uncertainty only adds to our fear, even if the risk, as a quantitative value, is very small!  Here we have an example of small risks attacked with big solutions that cost lots of money!

The marvelous water supply system of New York City brings some of the best tasting and safest drinking water in the world to nine million people, mostly in the city’s five boroughs.  It directs nearly 1.5 billion gallons per day (bgd) from a reservoirs system in upstate New York,  90% of which from the Catskill-Delaware systems about 90 miles from Manhattan.  The City is now spending approximately $3 billion to build an ultraviolet disinfection plant for the water supply, and to build a cover over the Hillview Reservoir, one of the last holding points for the supply.  That’s a lot of money, even in NYC!  What are we getting for it?

Except for the 10% from the East-of-Hudson reservoirs just north of the city, the water is unfiltered.  It is of such high quality, and spends so much time in enormous reservoirs, that it does not require cleaning.  Cities that draw their water from the ground or from rivers, gaaaggg!, must carefully filter the water.  The water is disinfected with chlorine to kill harmful bugs (pathogens), like the ones that used to cause cholera and typhus epidemics.  The water is safe!  Why the UV plant?

With the advance of public health science, new “disease vectors” have been identified.  In water supply, the latest are cryptosporidium and giardia, two very tiny critters that can cause intestinal disorders in humans, and if the victims have compromised immune systems, possibly lead to death.  These bugs are not killed by chlorine, but people can protect themselves by drinking boiled water.  They are very rare in NYC water.  There has never been a documented outbreak of any public health risk in NYC due to these bugs.  They can be serious risk in many small and improperly run water suppliers, especially those in agricultural areas, where farm animals produce lots of manure with the bugs that may get washed into water supply areas.  UV sterilizes the tiny bugs, preventing them from reproducing, which is as good as killing them.  Nobody has found a good way to kill them, other than boiling them, which is obviously impractical for 1.5 bgd.

So, we are spending $1.4 billion on a UV plant to eliminate a bug that is rare and impossible to monitor, which has never caused a disease outbreak in NYC, and from which the few at higher risk can protect themselves by drinking boiled water?  There was a serious outbreak about ten years ago in Milwaukee, but that system had a malfunctioning filter (which would normally capture the bugs) and happened during an extreme weather event that would not have a similar effect on NYC’s huge system.  In addition, NYC has a strict watershed protection program in place, which is why the US EPA does not require it to filter most of its water. 

Well, if you were at risk, you would certainly want to have that UV plant online!  But then, looking at it from the public health perspective, $1.4 billion would buy an awful lot of work in preventing TB, AIDS, veneral disease, and other sourges that are killing people now.  What’s the cost-benefit?

The story with the cover is much the same.  Birds pooped in the reservoir, the presence of E coli bacteria spiked, the EPA noticed it in the report and ordered a cover.  The problem was pretty much eliminated with other programs to frighten away and discourage birds, change the way water was withdrawn, etc, but the ruling was kept in place.  No exceptions.  $1.6 billion to build a cover for a reservoir that will not appreciable improve the lives of anyone but engineers and contractors working on it. 

Ahhh…but we can all breathe so much easier, knowing that at least the risk has been reduced to nearly zero!

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