Cottage Q&A: Pressure-treated docks and lake water

Published: December 9, 2020

A glass of water against a lake background By stocknadia/Shutterstock

Is it safe to drink water taken from the lake very near a dock built of pressure-treated lumber?— Ben Bichon, via email

The answer is a nebulous maybe. “It would really depend on the type of pressure-treated material and what contaminants are in it,” says Chris Sullivan, a senior project specialist with the environmental services laboratory of SGS Canada. The folks at Health Canada don’t recommend using any pressure-treated wood near sources of drinking water—wells and water reservoirs, for example. But if you’re talking about one dock in a decent-sized lake, anything leaching from the wood would become diluted, says Judith Weis, a professor emeritus at Rutgers University in Newark, N.J., who has studied the effects on marine environments of wood treated with chromated copper arsenate (CCA). Plus, the metals from this type of pressure-treated wood (copper, chromium, and arsenic) “tend to bind to sediments at the bottom of the lake.” Not helpful for creatures trying to live in the silt underneath a dock, but less risky for anyone drinking the water—even water pulled from the lake near the dock. Overall, the concentration of any possible contaminants would likely be low. “I certainly wouldn’t worry about it,” says Weis. “Lots of things in this world are more concerning.”

Is it safe to store drinking water in winter?

Like all the other stuff that might be in your lake. Never mind the metals that could potentially leach from your dock and potentially cause health problems in 10 or 20 years, says Jeff Zimmer, the manager of the Saskatchewan Research Council’s Environmental Analytical Laboratories. If you’re using lake water as a drinking source, you should be removing the expected baddies: coliform bacteria and other water-borne pathogens. “They’re going to be there,” says Zimmer. “And you need to get them out.”

Is our lake water safe to drink?

A UV system will kill pathogens, but to also treat the water for heavy metals, you’ll likely need to add a treatment system that includes a sand filter or an iron filter or that uses reverse-osmosis technology, he says. First step: test the water via a private lab (staff can advise you on how to best collect samples). Most municipal health units only test for bacterial contamination.

Got a question for Cottage Q&A? Send it to answers@cottagelife.com.

This article was originally published in the October 2019 issue of Cottage Life magazine.

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