Thursday, August 14, 2008

On drinking treated wastewater

I thought I should clarify my stand on drinking treated wastewater as I’ve been mulling it on and off over the past few days.

Basically, in my comment on a New York Times magazine article, I mentioned that the failure to detect any contaminants in wastewater does not necessarily imply that there are no contaminants whatsoever.

I still stand by that, as it is in the same spirit as the dictum “If all the swans that you see are white, it does not necessarily mean that all swans are white. Just one black swan will overturn your hypothesis.”

I followed that statement by stating that there may be some wisdom in mixing treated wastewater with untreated water, and allowing the mixture to percolate through layers of sand and gravel for months into an underground aquifer, from which it will be pumped out and treated again for drinking.

What I meant to say was that notwithstanding treatment, there still exists the possibility, albeit small, that there may be undetectable traces of unsafe, long-lived chemicals in treated wastewater. There are limits to any science, and it wasn’t so long ago that trans fat was accepted as being a healthy fat, or that PET bottles were blithely reused or that Nalgene bottles were praised (and then condemned). Who’s to say that, perhaps years after treated wastewater has become acceptable enough to drink straight from the faucet, scientists discover that we’ve been unwittingly accumulating alarmingly high levels of some obscure chemical along with our H2O?

Despite it being seemingly wasteful and irrational, it may be wise to hedge our bets and dilute treated wastewater with untreated but unpolluted lake or reservoir water, and then process the mix only after months of percolation through sand and gravel (where any long-lived chemicals would hopefully have broken down).

As a scientist and engineer, of course I’m aware of the irony of how sceptical I am towards drinking treated wastewater. I should be one of those championing reverse osmosis and all that newfangled membrane engineering technology! And not one of those Luddites advocating pumping the treated stuff back into the lake.

That said, I think I would be comfortable quaffing straight from the discharge tube of a clean Milli-Q dispenser. De-ionized, low TOC content and ultrapure, Milli-Q water is probably safer to drink than sipping from the water-cooler outside the lab.

[Of course, municipal water is probably not going to be treated to the same exactitude as Milli-Q water, and the Milli-Q dispenser does draw its ‘feedstock’ from a regular faucet, rather than the sewer.]

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