• Glenn Wilson
    Is the tap water in my home safe to drink?
    If there is no filtration of dissolved solids like arsenic then probably not. If there is no UV filter to kill living organisms then maybe not. The local standard for making home water safe to drink includes sediment filters, a UV light and reverse osmosis (RO). The sediment filters remove larger particles from the water which is nice in itself, but it is also needed for the UV filters to work right. The UV light is to kill living organisms (bacteria and virus). The RO system typically sits under the kitchen sink and has a separate water tap for drinking water. It is designed to remove dissolved solids in the water like arsenic. The UV light needs to be appropriately sized. If it is too small for the amount of water you use it may not do the job.

    Or, buy water to drink.

    For great information on local water quality visit the website of the charitable organization Caminos de Agua. See their site for Test My Water and
    Bacteria Testing (and list of local labs).

    If I wanted to install a sediment filter, UV light, and RO system for my home I would contact BCP Construction. You may know them as "Better Call Patty". A BCP Construction brochure is attached to this post and their email and phone number is in the brochure.

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    BCP brochure (846K)
  • Glenn Wilson
    Via email from our friends at Caminos de Agua (slightly edited):

    A reverse osmosis (RO) system is all you really need. It does not need to be used in conjunction with a UV light or any other kind of filter. An RO system will remove dissolved solids including As and F, AND all microbiological contaminants.
    Since contamination levels are constantly changing in San Miguel, we at Caminos de Agua recommend that if you do not have a reverse osmosis treatment system, not to drink the tap water.
    A solution that can provide safe and healthy water, and is the most sustainable solution long-term, is the collection of rainwater and then the simple microbiological treatment of this water (e.g. using a UV light, a Caminos de Agua ceramic filter, by boiling, etc.). We have more info on rainwater harvesting here.

    Their handy water treatment options (pdf file) is attached. Thanks for the clarification (of my post) and the info!
  • Glenn Wilson
    Two different neighbors asked me about this recently.

    A Reverse Osmosis (RO) system is typically installed under the kitchen sink and has a separate faucet for your drinking water.

    If you do not have an RO system you may have Arsenic or Fluoride in your tap water. As Caminos de Agua says: Since contamination levels are constantly changing in San Miguel, we at Caminos de Agua recommend that if you do not have a reverse osmosis treatment system, not to drink the tap water.

    The filter canisters that are commonly installed here do not and a UV light filter does not remove Arsenic or Fluoride. They both are useful and serve a purpose but they do not remove Arsenic or Fluoride. A Brita type filter also does not.

    To see a map of Fluoride / Arsenic levels for the SMA area see the map on the Caminos de Agua website (but the levels can and do change): https://caminosdeagua.org/en/water-quality-monitoring/.
  • Ron Lenox
    The map is very useful. I live in La Aldea and I saw my neighbor had her water tested. Showed Green! I plan to have mine done too. The more people that test their water through Caminos de Agua will improve the map.
  • Glenn Wilson
    What is the safe level of arsenic in your water? Zero.

    Arsenic is an element found in the Earth’s crust, and it finds its way into food, water, soil and air. In 2000, the U.S. Environmental Protection Agency considered tightening the drinking water standard for arsenic — then at 50 parts per billion — to as low as 3 ppb.

    Because of fears about the cost, the agency ultimately set the standard at 10 ppb, though it said there was essentially no safe level of the toxin. ...

    Some scientists believe there are harmful effects from arsenic below the drinking water standard. These include bladder, lung, liver and skin cancer, heart disease, strokes and diabetes. Recent studies have suggested that arsenic may cause IQ deficits in children and may be harmful to fetal development. ...

    If you discover that your water has arsenic in it, you can install a reverse osmosis filter next to your kitchen sink. Prices start at about $200.

    “It’s important to recognize that the current drinking water standard of 10 micrograms per liter was never claimed to be a safe level,” Smith said. “It is a risk-management decision that was made by U.S. EPA under the Safe Drinking Water Act that takes into account the health effects but also the cost of mitigating [them].”


    The problem is, according to the National Research Council, with “the current [federal] drinking water standard for arsenic of 10,” we’re not talking an “excess cancer risk” of one in a million people, but as high as “1 case in 300 people.” What? My 300 extra cases of cancer just turned into a million more cases? A million more families dealing with a cancer diagnosis? “This is 3000 times higher than a commonly accepted cancer risk for an environmental carcinogen of 1 in [a million].” “f we were to use the normally accepted” 1 in a million odds of cancer risk, the water standard would have to be like 500 times lower—.02 instead of 10. Even the New Jersey standard is 250 times too high. That’s a “rather drastic” difference, but “underlines how little precaution is instilled in the current guidelines.”

    Okay; so, wait. Why isn’t the water standard .02 instead? Because that “would be nearly impossible.” We just don’t have the technology to really get arsenic levels in the water that low. The technologically feasible level has been estimated at 3. Okay. So, why is the limit 10, and not 3? The decision to use a threshold of “10 instead of 3 is…mainly a budgetary decision.” Otherwise, it would cost a lot of money.

    So, the current water quote-unquote “safety” limit is “more motivated by politics than by technology.” Nobody wants to be told they have toxic tap water. If so, they might demand better water treatment, and that could get expensive. “As a result, many people drink water at levels very close to the current [legal] guideline,…not aware that they are exposed to an increased risk of cancer.” “Even worse,” millions of Americans drink water exceeding the legal limit: all these little red triangles. But, even the people living in areas that meet the legal limit must understand that the “current arsenic guidelines are only marginally protective.”

    Maybe we should tell people that drink water, i.e., everyone, that the “current arsenic regulations are [really just] a cost-benefit compromise, and that, based on usual health risk [models], the standards should be much lower.” People must be made aware that the “targets…should really be as close to zero as possible,” and that when it comes to water, at least, we should aim for the reachable 3 limit.

    How Risky Is the Arsenic in Rice?

    "..the National Research Council has estimated that the excess cancer risks associated with lifetime exposures to arsenic at the new US arsenic standard of 10 μg/l may be approximately 1 in 300. There may be susceptible subpopulations for which the risk is even greater."
    Reverse Osmosis Filter Use and High Arsenic Levels in Private Well Water
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