I recently had my water tested even though I have filters and a UV light. This is the El Salto water system that also serves parts of Volcancito. I was very surprised to receive the news that our water is contaminated with coliform, which most likely means the whole system is infected. In thinking through the breach in my purification process I realized that it most likely occurred during power outages. If you have a water system that has a pressure tank then you have noticed that you still have water for a little while even though your pump has no power. When the water stored in the pressure tank is used up, your tap runs dry. I regularly use my water this way, saving this last bit of running water for brushing teeth, etc. Well, it finally dawns on me...during a power outage.the UV light is not purifying the water that's running at this time and I am flooding my entire piping system with unclean water every time I do this. YUCK!!!
So, my next trip to David will include purchasing a UPS (battery backup) to install in the bodega for the UV light. Until that's installed I will not be turning on the tap during an outage. Live and learn.
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The UV light is the last thing the water passes through before entering the building. I will look at reconfiguring it to have it before the pressure tank, thanks for the idea. Also, we upgraded to a bigger light, the folks who built this house went too cheap and installed a 5 gpm light. Fillipo said to not run two major appliances at the same time and who knows how many times that has happened and the light was overwhelmed. Yes, we've already run bleach through all the pipes and will retest is a couple weeks.
A UV light on a UPS will definitely last long enough to use up the water in the pressure tank. The thing I need to guard against is the power of habit. I can't tell you how many times I reflexively hit a light switch as I enter a room during an outage. Same with turning on the tap, I want the light working for when I forget., or, don't realize the power went out if it's during the day.
I live on a farm that had a well contaminated with coliforms when we first arrived. The well is 35 feet deep x 30 inches wide likely. The lady at the water department informed me that wells need to be shocked twice a year to maintain a clean system. She suggested she felt I would have 1000 gallons in the well at any given moment in time and to add 3.5 cups of bleach to the well twice a year. Bleach does dissipate when exposed to the air after five min. So figuring out the size of your water tanks and adding the appropriate amount of bleach to add will help clean your system. One other person used the term flush. That person was right.
Boil your drinking water. It's the safest thing to do. You just have to bring it to a rolling boil, then turn off the gas. I stopped relying on the UV light after a similar coliform problem. I think the water passes through too fast for the UV to have time to kill a heavy load of bacteria, even when the light is working.