Based on recent test results here in Oregon and at the field trial in Uganda, we have decided to make some changes to our water box products. We are investigating adding a reflector on the inside surface of the tank lid, and we plan to increase the timer duration when external power is used. Details of these two changes remain to be settled, and depend on further test results. The timer duration has been increased from 1 minute to 2 minutes for the field trial. When the changes go into production, we will provide retrofits to current owners. The context and rationale for these decisions will be described in the remainder of this blog post.

Our target minimum reduction in microbiological challenge tests is 3 log (99.9%). In 2019, an independent lab (Aquadiagnostics Water Research & Technology Centre Ltd. in India) measured a 5-log reduction produced by a hand-cranked prototype water box. This year, tests at a different independent lab (Umpqua Research Co. in Oregon) were inconclusive as to the efficacy of hand-cranked operation,
and resulted in a 2.3 log reduction for a 1 minute exposure using external power.

In October we began a field trial in Uganda. The field trial protocol calls for testing source water for E. coli and total coliform levels before treatment and again after treatment, using Aquagenx test kits. Our Ugandan collaborators practiced with the test kits in the facilities of Engineering Ministries International East Africa (EMIEA). These practice tests revealed that the tap water in the EMIEA facilities was far more contaminated than was expected. To provide assurance of efficacy under those conditions, we doubled the exposure length from 1 minute to 2 minutes, and made a decision to deploy the water boxes only to test households which have electricity. We removed the crank handles so that the water boxes can only be used with external power. We expect to get the water boxes into test households in January.

Given the difficulty of getting consistent microbiological challenge test results from the local lab, we decided to measure the UV-C fluence (i.e. dose) delivered by the water box directly. Our target minimum fluence is 30 mJ/cm 2 . We have built 2 water boxes with quartz windows at different places on the bottom of the box, so that UV intensity measurements may be made after the UV light has passed through the water, without immersing the sensor. We are also trying to fit out a second sensor so that it is waterproof and can withstand immersion. These tests and measurements are a work in progress at the time of this writing.