Today, civil engineers make a deal with the Devil. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
We recycle most of our drinking water. We've used it before, and we must clean it before we use it again. We recycled water without cleaning it a hundred years ago. So typhoid and cholera were rampant. Then we added chlorine to city water systems. It worked. Typhoid and cholera are almost unknown in America today.
Then, in 1950, a new problem surfaced. Industries were dumping a lot of organic chemical waste into water systems. We were rid of germs. Now we had to get rid of those chemicals.
First we needed new techniques of chemical analysis to find out what was there. In 1974 two chemists solved the problem in different ways. A Dutchman, Johannas Rook, came out of the brewery business. He simply capped off a partially filled bottle of water and waited. Then he tested the air above it. That's the same way you find contaminants in beer.
The other chemist was Thomas Bellar with the EPA, an expert in air pollution. He bubbled clean air through the water. The contaminants were absorbed into the air, and he measured them. Rook and Bellar each obeyed the first principle of invention. Each brought alien expertise to the problem.
Then a bomb fell. Both Rook and Bellar made the same horrifying discovery. More chemical pollutants came out of the chlorinated water than went into it. Chlorine reacts to create new carcinogens. The worst of these is chloroform.
So we were rid of cholera at the cost of cancer. The government responded by putting a legal limit of 100 parts per billion on chloroform in our drinking water. That's still enough to cause one extra cancer death in 10,000 people who drink the water all their lives. The trouble is, we pay a price for getting even that low. We have to cut back on our use of chlorine until we're once more at some risk of water-borne disease.
By the way, you might wonder about fluoride. After all, it's a chemical cousin to chlorine. Fluoride is pretty nice stuff. Unlike chlorine, it doesn't react to produce anything nasty. And it's not a carcinogen itself. The traces of fluoride we put into water really do drastically cut tooth decay.
Chlorine is another matter. It tells the tale of our technology-dense world in microcosm. We trade a few deaths to avoid many. That's a not a deal we can accept in the long run. Since 1974 we've fought it. We've brought millions of dollars to bear on the problem. We haven't beaten it yet, but we will. Because, after all, solving that kind of problem is what engineering is all about.
I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.
(Theme music)For a quick and useful look at drinking water you may write to
Prof. James M. Symons
Civil Engineering Department
University of Houston
Houston, TX 77204-4791
He'll send you a set of notes he's prepared for freshman engineering students. The title is Plain talk About Drinking Water.
For more detail about the present case see
Symons, J.M., Bellar, T.A., Carswell, J.K., DeMarco, J., Kropp, K.L., Robeck, G.G., Seeger, D.R., Smith, B.L., and Stephens, A.A., National Organics Reconnaissance Service for Halogenated Organics. Journal of the American Water Works Association, 67, 11-Part 1, Nov. 1975, pp. 634-647. (See also Update, 67, 12, December 1975, pp. 708-709.)
or
Symons, J.M., This Week's Citation Classic. Current Contents: Agriculture, Biology & Environmental Sciences, Vol. 19, No.33, August 15, 1988, pp. 14.
See also a handbook on halogen treatment of drinking water prepared by a group of leading environmental engineers:
Treatment Techniques for Controlling Trihalomethanes in Drinking Water. American Water Works Association, 1982.
Our water in Houston contains less than the mandated limit of chloroform -- 100 parts per billion. That leaves us at somewhat greater risk from pathogenic microbes, although we meet government standards there as well.
Some cities violate the standards and let chloroform run to 300 ppb. That assures safety from pathogenic microbes. But it also threatens three cancer deaths in every 10,000 people.
Of course, these numbers are trivial in comparison with other carcinogens. We accept vastly greater damage from tobacco. Even second-hand smoke inflicts far more cancer than drinking water ever does.