If you want to be really stringent...

from the copepod department:

How's this for a chumra?

Water Filters Rely on Nanotech
AMSTERDAM -- A slow, methodical transformation of the $400-billion-a-year water-management industry is currently in progress, and nanotechnology appears to be leading the way.

...

The promise of nanofiltration devices that "clean" polluted water, sifting out bacteria, viruses, heavy metals and organic material, is driving companies like Argonide and KX Industries, which developed technology used in Brita filters, to make nanotechnology-based filters for consumers. Two products incorporating nanotechnology are going to hit the market within the next year and are already being tested in developing nations.

"Nanowater is extremely exciting," said KX Industries President Kevin McGovern, emphasizing that 1.3 billion people do not have access to safe drinking water and past trends indicate that global consumption of water will likely double in the next 20 years. His Matrikx water filters will be on store shelves within the next year after already having experienced success in 50 pilot programs throughout central Asia.

Argonide's president, Fred Tepper, is trying to get his product in the hands of consumers in the next 60 to 90 days, he said, having recently secured a distribution deal with a European company.

Both companies claim their products are the first filters to block the passage of bacteria and viruses across a nanofibrous membrane effectively, making potable water available for people in places like Bangladesh who face horrific deformities due to high levels of naturally occurring arsenic in the water supply.

Though these breakthroughs seem cutting-edge, the technology is not terribly new. Water-treatment plants have been using nanofiltration and ultrafiltration membranes to separate good water from bad for more than five years. And already the technology is becoming the industry standard.