Water district lab gets high marks for finding pathogens

It’s no accident that when you turn on your tap in Santa Clara County, clean water comes out. It’s the result of hard, exacting work that the Santa Clara Valley Water District undertakes to ensure that we provide safe, clean water that supports life and the economy here in Silicon Valley.

To do that, we have a state-of-the-art lab that is consistently rated near the top in the country for its ability to detect water-borne pathogens. The water we produce here in Santa Clara County consistently meets or exceeds all state and federal drinking water standards, which are getting increasingly stringent as new technology develops.

Senior Microbiologist Chris Carbone demonstrates the start of the process to detect giardia and cryptosporidium.

Particularly difficult to detect are giardia and cryptosporidium. These microscopic parasites can cause extremely bad diarrhea, which can result in dehydration that children, the elderly and those with compromised immune systems may not be able to handle.

So detecting these parasites is important to keeping our water supply, and the people of our county, safe. The water quality lab’s ability to do that was tested late last year during proficiency testing managed by the Wisconsin State Laboratory of Hygiene. In that testing, the water district ranked second out of 54 participating labs nationwide.

That means that the district’s lab and employees were among the top labs to recover these organisms in unknown water samples.

The proficiency test gauges whether the staff, equipment and processes can find the pathogens and if so, how many. The process begins when the Wisconsin State lab sends a 10-liter sample of water to the lab doing the testing. It’s a blind sample, meaning the water district biologists don’t know what they’ll find. The sample could have no parasites; it could have just giardia or just cryptosporidium, or it could have some of both. It will also include background items like algae and debris.

vortexer shakes up tiny vial
The vortexer is about to shake things up.

Then a process to remove the background materials and make those 10 liters small enough to fit onto a slide begins. It involves running the water through a filter and agitating the sample in various ways – through a centrifuge, through a manual shaking movement described as a “grenade toss,” and through a “vortexer,” a small device that sounds more sci-fi than it looks. There are buffered solutions, antibody-coated beads and magnets used to separate out the cysts.

Eventually, the whole process results in 0.5 milliliters of liquid applied to a slide, which is then dehydrated and stained with fluorescent stains specific to cryptosporidium and giardia. The stains help the scientists to differentiate between the target parasites and other background items that might still have gotten through the filtering, agitating and magnetizing.

Those glowing spots on the screen are cysts.

The sample that the water district tested had 154 cysts in it, and the water district lab found 125 – a significant recovery.

Our lab consistently performs near the top in such tests. Following a cryptosporidium outbreak in Wisconsin in the early 1990s, major utilities across the country had to submit results from monthly sampling of the water from each water treatment plant to the federal Environmental Protection Agency for two years. In order to submit those results, our lab had to be certified for cryptosporidium analysis. The water district lab achieved that certification in the mid-1990s, one of the earliest labs in the state to do so. Our water district lab runs tests monthly on the raw, untreated water coming into the treatment plants, as well as on reservoir water.

The other part of the pathogen puzzle is treating the water. Ultraviolet light, ozone and hydrogen peroxide deactivate the parasites. The water district’s Santa Teresa and Penitencia Water Treatment Plants are equipped with ozone, and the Rinconada Water Treatment Plant will be when its upgrade is complete.

The water district’s lab performs more than 170,000 tests each year on raw and treated water from our various sources. Senior Microbiologist Chris Carbone, who conducted the high-performing test, noted that ongoing improvement has been a part of the culture of the water district’s lab for years.

“We want to continue to improve and get better at the things we do,” he said, and acknowledged that the new employees coming into the lab will help advance that trajectory into the future.

1 comment

  1. Thank you for protecting our drinking water! Everyone want to feel their tap water is safe to drink. And congratulations on your high ranking in the testing exercise.


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