For decades, sewage has been treated and used for irrigating crops, parks, and golf courses, but making it fit for human consumption requires a much more rigorous filtration technology using polymer membranes. No thicker than a human hair, the membranes are at once delicate and durable. Using pores smaller than one-millionth of a millimeter, they’re capable of wiping out microscopic contaminants. ... the water division at Dow Chemical, he pulls in more than $1 billion in sales annually. The membrane market is growing more than 10 percent a year in part because of increasing water scarcity worldwide and ever more pressure to develop drought-proof water supplies from new sources. ... The whole concept of recycled sewage might be harder to swallow if there weren’t already so much sewage in the water sources we routinely draw from. ... the very reason chemists created these synthetic membranes decades ago is that, increasingly, humans have been contaminating the water supply. Industries have emerged, meanwhile, that need purer water for manufacturing. Most major players in the automotive, beer and wine, food processing, petrochemical, pharmaceutical, and semiconductor industries, for example, rely on water purified by membranes. ... recycling wastewater is about half the cost of desalinating ocean water: Both use RO membranes, but the salinity of ocean water is much higher, so it’s harder and much more energy-intensive to pump it through the tiny holes.
In the US, municipal drinking water is protected by the Safe Drinking Water Act, which compels utilities to monitor things like microorganisms and the disinfectants used to subdue them. In 1998 the EPA tightened its standards on disinfectants, many of which can have their own toxic byproducts. One of the worst offenders is a classic: chlorine. Its main replacement, a chemical called chloramine (really just a mix of chlorine and ammonia), has lower levels of carcinogenic breakdown products, but it also makes the water corrosive—enough to eat through metal. ... Lead is insidiously useful. It’s hard but malleable, is relatively common, melts at a low enough temperature to be workable, and doesn’t rust. The Romans used it for plumbing—in fact, that word derives from the Latin word for lead, plumbum. Even the Romans noticed, as early as 312 BC, that lead exposure seemed to cause strange behaviors in people. But as Werner Troesken, an economist at the University of Pittsburgh, explains in his book The Great Lead Water Pipe Disaster, lead pipes solved a lot more problems than they caused. The hydrologists of the 19th century knew that lakes and wells could harbor cholera; they needed large, clean bodies of water that they could pump into the city. Lead made those pipes possible. ... in 1991 the EPA instituted the Lead and Copper Rule, requiring utilities to check water regularly. The critical level has changed over the years as new science has come to light, but today officials are required to take action if lead exceeds 15 ppb in more than 10 percent of residents’ taps. The metric is utilitarian, scaled to spot trouble just before it turns into disaster. It’s a good rule, as long as utilities follow it.