March 15, 2022

by Dave Conklin

It wasn’t what we wanted to hear. On February 19th we received a report from the independent Oregon lab on their fourth round of water box testing. This report showed worse performance than in the previous round of testing, and, like the previous rounds, was internally inconsistent. There were five tests performed; three gave results that didn’t make sense to us:

    1. Test #1 is a control, where water placed in the box and removed after 10 minutes is never exposed to UV light at all. Before and after samples are analyzed to measure whether the box itself without the light affects the MS2 surrogate pathogen. This test had also been run in the second round; the result in the second round was 2.1 x 106 before, and 1.8 x 106 after, a difference less than the measurement uncertainty. It has also been run in the first round, yielding 1.3 x 108 before and 9.7 x 107 after, a slightly larger difference but still within the measurement uncertainty. The fourth round results for the control are 1.8 x 107 before and 3.3 x 107 after, a larger difference but still within the measurement uncertainty, but notably a difference going in the opposite direction from the previous two similar tests. The viral load measured after was nearly twice that measured before.
    2. Tests #2 and #4 were duplicates using 120 seconds of UV exposure. Test #2 resulted in a log reduction of 0.9 and test #4 a log reduction of 0.8. Both results were disappointly low, but at least they were pretty consistent with each other. We had established a target log reduction of 2.5 before the test, based on a result of 2.3 log reduction at 60 seconds exposure in the second round of testing. The puzzler was the results from tests #3 and #5, another pair of duplicates but using 180 seconds of UV exposure. The lab has told us verbally that tests #3 and #5 appeared to go normally, but test #3 resulted in a log reduction of 0.7, essentially the same as for the tests at 120 seconds of exposure, and test #5 got a log reduction of 0.0, i.e. no reduction at all.

So the result of test #1 is odd compared to previous rounds, but still within the + or – 0.5 log reduction measurement uncertainty, while tests #2 and #4 are inconsistent with the result from the second round, and tests #3 and #5 are inconsistent both with each other and with #2 and #4… longer UV exposures should always result in greater reductions in the test organism, and a duplicate test ought to produce a similar result.

The microbiological challenge tests at an independent lab are one part of a 3-part program to confirm the effectiveness of UV water treatment using the water box. We’ve had more success with the other 2 parts, which are model calculations and field testing for coliform bacteria. The lab challenge tests have been done at 2 different labs, and the results have been inconsistent – sometimes quite good, sometimes OK, and sometimes not OK at all. The puzzling part has been that sometimes the lab results just haven’t made sense. Increasing UV exposure time should always produce a greater reduction in the microorganisms, but some test results indicated the opposite. Repeating the procedure using the same inputs and water box should produce similar results, but sometimes it didn’t.

DayZero Products and the Water Box Volunteers group are working together to field test and improve the water box. (See for more information about the volunteer group.) After receiving the most recent lab report, the Volunteers held a brainstorming session on Zoom. We decided in that meeting that we needed to find some expert help, and identified 5 potential sources: the Oregon State University microbiology faculty (Corvallis OR), the Pacific Northwest National Lab (Richland WA), Carollo Engineering (Portland OR), Jacobs Engineering (formerly CH2M, Corvallis), and Aqua-Aero WaterSystems (Delft, Netherlands). Several of those sources have been potentially helpful. Carollo, in particular, is giving us a lot of help and was quick to identify a possible cause of our inconsistent lab results. The test spec that we provided to the labs specified that the MS2 test organism should be mixed into distilled water. The expert at Carollo has advised us that the influent solution, if prepared with distilled water, should include a buffer, and further that MS2 is a notoriously tricky species to work with. We’ve been advised that there are only a few labs in the world that do the MS2 assays routinely and reliably; our next round of lab testing will use one of those.

We are relieved that we may have located the problem, looking forward to working with a lab that can do the tests we need, and optimistic that the next round of tests will give consistent and encouraging results. We hope to update the blog with those results soon.