Drinking Water Quality in Merida and Yucatan

November 20, 2019
The issue of drinking water quality keeps coming up over & over on Expat web-boards, webpages, and Expat FB pages, for at least the past 14 years.

The common ~lurid rumor~ that many newbies propose is that our Merida City tap-water is somehow ~magically~ “bad” …

Fortunately, the opposite is true. … Merida City tap water consistently tests clean roughly 97% of the time, when tested before the water enters the home. … Sadly, so many Merida homes have contamination in their tinacos** and cisterns** that just 75% of Merida homes test clean at the kitchen sink tap. *  (See below for instructions on inspecting your home water system quality.)

Continuing… Why is Merida tap water so clean, but SO HARD??

Our Merida City Water (JAPAY) comes from 130 ft deep wells … and it’s from 10 million years ago. … Were there pesticides & herbicides 10 million years ago?

Since there is 100 feet of limestone between modern surface water and our 130 ft deep Merida City drinking water wells, there really is no practical way (route) for surface contamination to get down 130 ft to our drinking water supply. … Merida is not New Orleans whose Mississippi River contains the effluents & sewage & feed-lot & farm run-off from the Rocky Mountains to the Appalachians… like in the USA & Canada (tar sands & fracking) …

USA water??One of the earth's most polluted rivers

Not Merida … 😉

Fortunately, here in Merida … We have no tar-sands oil… We have no fracking .. We have no Mega-hog farms or Mega-chicken farms … No big chemical plants nor refineries …  and there’s NOBODY “upstream” from our drinking water …

=> Remember … USA-nians are justified to fear the over 5,000 USA water districts** who have been failing US EPA standards for years … But those fears simply do not fit Merida. … Seriously … It’s US drinking water that people should fear.


Image result for dirty refinery

Again … 40 years of Scientific Testing show … It’s USA water we should fear …   That’s the USA … Think Michigan ..  New Jersey ..  Texas … Louisiana … Chicago .. Pittsburgh

Fortunately, Merida City JAPAY water is proven clean at 97% of the homes tested***, when it enters our homes.

**The water for Merida City wells at 130 ft depths is very clean … but it is very hard (High calcium carbonate levels – which are NOT a health risk – but just taste a bit “off”)…   Why is Merida city water so clean? …. because that water is 10 million yrs old … and there were no pesticides 10 MILLION years ago.

*       *       *       *        *
***Past independent studies show clean Merida city water 97% of the time, ~ENTERING~ the house … but that water entering the house … is not the same as water at the kitchen faucet … That means that roughly 25% of the water tested in Merida kitchen sinks had microbial contamination (fecal coliforms) FROM INSIDE THE HOUSE’s plumbing.


No dead birds … no dead ‘possums … no accumulated leaf litter … SERIOUSLY … people leaving the tops of their cisterns & tinacos open is THE REAL ISSUE, per 20 yrs of test results.

and yes, Virginia … You can test your own water!
~ Note that if you test the water coming into your Merida home  for free-Chlorine (swimming pool test kit) … and if you measure chlorine present – then your water is FINE !

= = = = = = =
Next:  Are you unsure about the quality of your Merida City water in your tinaco or cistern ?

*Tinaco~Cistern Inspection & Maintenance:
For people on Merida City water (JAPAY) … Basically … LOOK in your tinaco~cistern    and  ~sniff~  it. 😉

If you see organic detritus (dead leaves, dead rotting vegetation, dead birds, dead iguanas, or roots) … then REMOVE all the detritus, rinse it out … and disinfect it with normal laundry bleach**.

If the tinaco~cistern water looks clear & clean, and smells OK, then it’s 97% likely OK … And yes,  some accumulated “sarro” … scale … is OK.

To ENSURE it’s OK, you can add enough ordinary laundry bleach** to disinfect it: … ¼ cup of bleach per 1,100 liter tinaco (300 gal) … completely eliminates bacteria, viruses, microbes. … This free-chlorine concentration is equal to a US public swimming pool … (for about the next 2 days). 😉

After adding the bleach, mix the water gently … and wait 15 minutes. … Then flush the toilets, run the sinks & showers … etc to fill your all of your home’s pipes with the nice free-Chlorine disinfectant (bleach) …
Image result for glass of clean water
Allow that water to stand for about 15 minutes … to kill everything that may have accumulated in the pipes.

Then …. use the water as normal.  … Note that there will be a light chlorine smell (like a swimming pool) for the next 2-3 days => thoroughly disinfecting your home’s plumbing !

**Use ONLY normal plain dull household-laundry bleach .. Not scented bleach … Not “Gel-no-splash” bleach … Just normal household bleach.

*       *       *       *        *
As long as you have a good top on your tinaco~cistern, this bleach treatment is likely needed only about twice a year. … If you get dead birds, dead possums, dead iguanas or dead leaves in your tinaco~cistern, in the meantime … then start over. 😉

*       *       *       *        *
What if you are not on Merida City JAPAY water?

If you are drinking private well water from TOO SHALLOW wells across Yucatan – or drinking cenote water … then all bets are off. 😉

If you are drinking well water from a TOO SHALLOW well, dump a bottle of blue food dye into the toilet … flush the toilet … and turn on all the faucets in the house for about 10 minutes … collecting the water into white containers (like a white bowl) …  then wait 30 minutes,  and run your kitchen sink water again into a white bowl  (and flush the toilet) … and look for blue …

Image result for dirty full septic tank

The first 30 ft of ground water here ACROSS YUCATAN is often contaminated … most often by private homes septic systems.   … That means shallow wells are a problem, but GOOD wells drilled to 18m – 20m almost always have hard, but clean  water …    Why?? … Note that our BIG hard limestone aquatard between 30 ft to 60 ft (20m) ~blocks~ surface contamination from reaching even private wells drilled to 18 – 20m.

Final note … A literal 47 years of scientific measurements show there is very little horizontal (sideways) movement of ground water in Yucatan, with 2 exceptions.*   … Notice that there are NO mythical “underground rivers” flowing in almost all of Yucatan. … 47 years of measurements shows that most (95%?)  of our surface water moves vertically through our limestone.

Notice that if there was lateral-horizontal movement of water in the caves that connect cenotes … then the sediment in this channel would be stirred up by the flow of the mythical “underground river” …

No flowing river here… just quiet still water ..

*The 2 exceptions to “no under-ground rivers”:   

Near the coasts, the rainwater in the first 10 km – 15 km of rainwater does slowly move out towards the sea.   and … In the hilly areas of Yucatan – like Campeche & Bacalar – the rain water does move downhill underground …

But notice how slow the flow is … from how clear the happy diving-girl image is. 😉

Don’t worry …. Be happy …

You’re in Yucatan! ….. Enjoy!

*           *           *           *

Feel free to copy while giving proper attribution: YucaLandia/Surviving Yucatan.
© Steven M. Fry

Read on, MacDuff.

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20 Responses to Drinking Water Quality in Merida and Yucatan

  1. yucalandia says:

    Dr. Fry here …
    Another issue also comes up in the 14 yrs. of expats questions about water quality in Merida and Yucatan:
    ” Who are you to make such claims? ” and “Can you please tell us your educational & technical background?”

    So … To put out any fires while they’re still small:
    I’ve been fortunate to work at some of the best labs in the USA – with some really fine fine top-drawer people …

    Remember when the Big Oil companies were forced to take lead out of gasoline?
    I was fortunate that one of my first professional chemical-environmental jobs was to test samples for the landmark Illinois Lead Project – a program that ultimately saved 200 million or so Americans from living with lifelong lead (Pb) contamination from gasoline motor fumes.

    I was similarly fortunate to work testing samples & consulting for all the US Army’s big contaminated sites, all the US DOE big contaminated sites (like Los Alamos, Rocky Flats, INEEL, Hanford, Oak Ridge, Cape Cod, etc), and the US Air force’s worst sites … where another 100 million Americans living down-wind and down-stream of these very contaminated sites, lived healthier lives, drank healthier water & breathed healthier air as a result of our lab’s efforts.

    Our scientific work for the benefit of yet more literal millions continued in Ukraine, and most recently here in Yucatan – evaluating Dengue risks – tracking Dengue & tracking mosquito control efforts …

    So … It’s been a good life.
    (Dr.) Steven Fry

  2. yucalandia says:

    Ooooops …

    I just realized that I left out the answers to the people who asked about my educational background & professional training, that created the foundation for writing the article above:

    I started as a water testing professional in 1976, at the Univ. of Illinois … working on the Illinois Lead Project**, plus testing water quality in every new commercial well drilled in Illinois.
    In the 1980’s I completed a Ph.D. in Analytical Chemistry, Water Quality & Public Health … at Colorado State University.

    In the 90’s I authored, developed & published 7 different EPA methods on water quality.
    After the breakup of the Soviet Union, I was the first Western Scientist invited into former Soviet Union, to help them solve their SERIOUS REAL water & food contamination problems (Ukraine, Belarus, Tajikistan, Moldova).

    I was an owner-operator of the USA’s highest ranked Environmental Testing laboratory, with 75 employees, testing samples for every single major DOE and major DOD site across the USA. We served as a certified lab for 34 States, Los Alamos, INEEL, Hanford, the DOE, the Navy, the Army Corps of Engineers, and the Air Force. … plus consulting on Environmental programs in Scotland, Mexico, Canada, & Italy.

    I then moved to Merida full-time in 2006, where I was invited to serve UADY’s biggest laboratory, working on big Bill & Melinda Gate’s Foundation grants & then big US National Institute of Health grants, monitoring mosquitos and Dengue in 1,500 poor people’s homes across Yucatan State.

    While in Merida, working on Dengue & water quality issues, I was also a Staff Editor for 7 yrs for UADY’s “Revista Biomedica” … Bio-Medical journal … 😉

    Enjoy a good glass of clean water … on us.

    Happy Trails!

    • Rick says:

      Rick’s Second Round of Emotive Musings:

      “I know people who were even president of their respective countries, and yet were totally useless or incompetnet at the job. A degree is no guerentee of integrity. You lost all integrity when you used a picture of the Ganges river in india to highlight your so called knowledge of American water supplies. A fraud will always be a fraud. ”

      ” I have been engaged in issues of contaminated water for decades and have found mexico to be one of the worst experiences I have ever engaged with water. By the way, microscopic bugs have been about for 260 million years that science knows of. Pesticides can be the least of your problesm, if you care to look in the right corners. While reporting that “waters are highly likely to be contaminated” may be a big call… scientific evidence from multiple sources are what lead people to make accurate assumption as against people who test only releatively small samples of such huge volumes of water as you have stated. But once again…not going to argue with a fraud…fraud is the creation of an illusion to establish your point…such as the Ganges to illustrate American waters. If you dont know your rivers, you know Jack shiite about water supply and contamination. Cheers…you drink that water yourself…gives me the shiites every time bar none. Bottled water still remains one of Meridas biggest sellers for a reason. ”

      = = = = = = =

      Educated Reader’s can note that Rick completely ignores the most complete, independent – UADY University conducted study of Merida City tap water that showed that over 97% of Merida homes receive very clean, pure-but-hard water at their JAPAY water meters. When 97% of a city’s homes tap water tests clean by proven reliable scientific testing, should we really believe the rants of cranky guys like Sr. Rick, who have no data … no studies … & no facts to back up their highly emotional personal claims?

      Sleep well everyone,
      Dr. Steven M. Fry

  3. Alan Sutherland says:

    A photo of the Ganges River while describing water quality in the US is misleading. A report from Geofisica International (2000) Vol. 39, Num. 4, pp 359-365 disputes your information. Granted this is an old report, but unless their recommendations were followed we are still lacking clean water.

    • yucalandia says:

      We love data here.
      Notice that the report you quote has no test results … from actual drinking water samples from Merida’s City tap water. … The present zero evidence that shows the City water at your Merida kitchen tap is supposedly contaminated.

      I read your supposed UNAM (Mexico City) study of Merida water … by Mexico City guys who tested ZERO water samples (no testing of any kind) ... and I suspect you did not notice the key details what they wrote:

      Mérida currently obtains about 65 % of its drinking water supply from the JAPAY-1 well field which draws water from the southeastern section of the city, where most of Meridas industrial activity is concentrated. No information is available on the water quality from this well field, ”

      ” … ~ but it is likely~ to be also heavily contaminated.

      No actual test results, but they announce a supposed BIG conclusion that
      (Merida’s biggest well field) is ~ likely~ to be heavily contaminated ” …

      Seriously? … This sort of “research” borders on false reporting to panic people … 😦

      Every single reputable study we’re read on Merida City drinking water shows that, BEFORE the City-water enters the home, Merida water tests clean.

      Please, give us some links or copies of real reports that actually document the water quality … especially reports that test 100’s of homes in each and all of Merida’s different water districts.

      Looking forward to some real scientific results … NOT guessing & hand-waving by UNAM guys –

      UNAM guys who actually did NO testing of water samples ... . 😉
      Happy Trails,

    • yucalandia says:

      Have you read the study you based your view on?

      How does it dispute our information? … We described contaminated water in the upper water table, but clean water below 18m – 20 m. … while Merida drinking water wells are drilled to 100m.

      Notice when we similarly drill down into the UNAM paper, it does NOT say that Merida drinking water actually tested positive for contaminants … instead it vaguely talks about “ground water”:

      “Vázquez et al. (1997) identified dissolved organic compounds in the aquifer underneath Mérida. They found of the following compounds up to 10µg per liter:1, 1, 1 -trichloroethane (TCA), trichloroethene (TCE), tetrachloroethene (PCE) and carbon tetrachloride (CTET). ”

      Notice that these contaminants were NOT found in any drinking water samples …

      Then notice that the UNAM guys claim that
      “… piping and discharging the untreated sewage to the ocean 33 km from Mérida, and (3) using the untreated sewage to irrigate gardens around Mérida”

      somehow magically might get into our 100m deep well water.

      Do you really believe that sewage discharged out into the Gulf … is being piped into our Merida homes?

      Do you really believe that a little untreated sewage on gardens around Merida … is getting into our water being pumped up from 100m ?


      Then notice their 1995 report of Cd, Cr, and Pb were NOT in Merida drinking water … but again in ground water:

      ” Cadmium (17.6 µg/1), chromium (2.8 µg/l), copper (1233 µg/l), lead (87.5 µg/1) and zinc (6690 µg/1) have also been reported in the ground water of Mérida in the industrial zone.

      Seriously … Every single report that purportedly finds problems with Merida drinking water … does NOT stand up to even mild scrutiny. 😦

      Happy Trails,

  4. yucalandia says:

    A friend on FB just wrote:
    ” I do wonder why people are constantly freaking out about the water!? ”

    My reply:
    .. Drama …
    Some people need some ~drama~ to spice up their life,
    plus we’re about 40 years into a cycle of the Press no longer doing the hard work of journalism, where, from Reagun onwards, they instead choose to repeat what the politicians tell them….
    Politicians & Big Media love to scare us … to try to create false dependency on them …
    and finally … It’s WAY BETTER gossip (chisme) to tell ~lurid~ stories about how DANGEROUS Merida city tap water is.

    … It’s a pretty dull story, to say … Yeah, our water is OK … REALLY HARD … but generally OK.

    • Rick says:

      Editor’s Notes:
      Rick’s comments below are neither accurate nor factual nor supported by medical science.

      Before reading Rick’s latest wild rants, instead consider the facts:
      ~ A person would have to drink over 44 glasses a day of Merida City tap water to equal the calcium in just one daily Calcium dietary supplement pill.

      ~ It has long been scientifically proven that Yucatecans, Guatemaltecans, El Salvadorans & Costa Rican workers too often do NOT drink enough fluids, and they have been suffering 25% to 300% higher rates of diabetes, kidney disease and urological problems due to dehydration as Climate Change has made temperatures across Central America hotter every year this past 20 yrs.

      So… Please read the following comments below, knowing that they are written by a non-scientist who does not know what they are talking about, as he substitutes old wives tales & common internet-rumors… in place of proven science & proven medicine.
      Dr, Steven M. Fry
      We hope that the following amateur musings (by Rick) are enjoyed by at least some readers – in a humorous vein – and that the musings & emotings should not be taken seriously in any way, shape, or form.

      For factual context … notice how in “Rick’s” world,

      ” Water testing is a trained monekeys job. ”

      “By the way, microscopic bugs have been about for 260 million years that science knows of. ”

      and our personal favorite:

      ” (Ingesting) pesticides can be the least of your problesm, ”

      and yes… We heartily welcome anyone who can tell us what “microscopic bugs” are, and what “monekeys” are …
      … Dr. Fry

      = = = = = = = = = = = = = =
      Rick’s Musings:
      Among Mexican´s, a good percentage consume hard water, which is considered to be a significant etiological factor around the globe causing many diseases such as cardiovascular problems, diabetes, reproductive failure, neural diseases, and renal dysfunction and so on. Merida is not an exception. Any fool can test water….most people do it in the swimming pool. Dont need to be a rocket scientist as you attempted to make yourself out, to do that. What you do not have is the medical background to know what to look for in the systemic illness´s that abound around you. The people of Merida may have been better off health wise without your unknowledgeable input for last so many years. Water testing is a trained monekeys job. General health and repercussions of contaminated water is not. I have doctors and Bio chemists in mexico who disagree and laugh at your claims periodically. You are not in the same league as them. But hey…your ego trip stories about home purifiers and such are entertaining. Think you have been drinking too much of the local water, among other things. – “It’s a pretty dull story, to say … Yeah, our water is OK … REALLY HARD … but generally ” – dont know who you think you are kidding lol…but I know…..yourself!
      = = = = = = = = = = = = = = =

      G’nite Rick… Now that you’ve got all they off your chest, we hope you sleep well.
      Dr. Fry

  5. yucalandia says:

    Drama (cont):

    Some additional Context on the information above?
    Back in 2007, I had a British friend here who literally bought the last 500 home water purification units (of a USA company’s previous line) – at a big “closeout” discount … with his BIG PLAN to make beaucoup $buck$$ by selling home water purifiers to Mexicans in Merida.

    he peculiar thing? … When he tested for “residual free chlorine” at his customers kitchen sink taps, he kept finding measurable but safe chlorine-disinfectant levels.

    Merida home after home after home … inconveniently … had clean water that the kitchen sinks he tested … which meant he ultimately had to give up trying to sell all his (bought-on-the-cheap) home water purifiers.

    Merida home after home after home … had clean water at all the kitchen sinks he tested … which meant he ultimately had to give up trying to sell all his (bought-on-the-cheap) home water purifiers.

  6. Alan Sutherland says:

    Where are your test results? Past independent studies?

    • yucalandia says:

      Yes, I prefer the big independent UADY study of JAPAY water, testing water as it enters 364 Merida homes & at their kitchen sinks.

      Notice that the study you cite had NO tests of actual tap water, at actual homes. Then notice that the study you cite … similarly cited other studies that also did NOT test actual tap water, at actual homes.

      It’s difficult to believe (supposed) studies on (supposed) drinking water-quality, when the people do not actually test drinking water samples.

      It’s especially difficult to believe lurid emotionally-charged claims & emotionally-charged conclusions, when they did not actually test city of Merida drinking water in people’s homes.

      Testing a few samples near surface “ground water” (at depths – unrelated to Merida’s deep wells) does not say anything about actual Merida drinking water quality that we drink

      … especially when the authors of those small non-representative samples make claims that do not fit with the last 3 decades of actual scientific test results of real Merida Japay drinking water.

  7. andreas montoya says:

    The City of Merida, in the State of Yucatán, obtains its drinking water primarily from three well fields located in the periphery of the city. In addition, there are water supply wells within the city. Water from the public water supply contains lead, cadmium, chromium in excess of the Mexican Drinking Water Norm. The following organic contaminants have also been identified in the ground water in the southern portion of the city: TCA, PCE, TCE, and carbon tetrachloride (CTET). TCA, PCE, TCE and CTET are all pesticides or herbicides some of which have been banned in other countries. Mérida currently obtains about 65 % of its drinking water supply from the JAPAY-1 well field which draws water from the southeastern section of the city, where most of Merida’s industrial activity is concentrated. No information is available on the water quality from this well field, but it is likely to be also heavily contaminated. A ground water monitoring scheme is suggested. A hydrogeological reserve zone should be established to allow the inhabitants to have a sustainable source of drinking water. The TCA, PCE, TCE and CTET are all pesticides or herbicides, some of which have been banned in other countries.

    Click to access 61ead4a73bbe8e6ac11232edc5b5bb7fbb50.pdf

    • yucalandia says:

      Notice that Mr. Montoya mixes two very unrelated facts into the same idea space.

      Andreas introduces the fact of 3 VERY DEEP water JAPAY City water well fields. … but then immediately and falsely tries to convolve it … using falsely~scary-ways~ … to make deep well water somehow, magically the same as GROUND WATER near-surface contamination.

      Montoya misdirects with facts … facts that have NO BEARING on City of Merida JAPAY water:
      He announces:
      The following organic contaminants have also been identified in the ground water in the southern portion of the city: TCA, PCE, TCE, and carbon tetrachloride (CTET). TCA, PCE, TCE and CTET are all pesticides or herbicides some of which have been banned in other countries.

      Notice that Montoya plays the same scare-tactics games that other local publications have played for the last 10 years … where they falsely equate a few small pockets of a few neighborhoods near-surface ground water (in the first 25 ft) … falsely equating a few near-surface water problems … with our 160 ft deep City water wells.

      What does it say … when someone intentionally tries to mislead people?

      What does it really say … when someone intentionally mis-uses facts … and misquotes legitimate studies … attempting to (unnecessarily) SCARE people ?

      Real scientists … honest scientists … honest reporters … do not play such ugly games.

  8. John says:

    My question is where can you have your tap water tested here in Merida?

  9. Bawb says:

    Some of the arguments are a bit thin.

    Just cos the well is130ft deep doesnt mean the water is 10M yrs old. Mixing will occur and the rainwater that flows (very rapidly) down into it (the cracked limestone makes for very fast run off) will certainly mix with whats down there, esp when you’re sucking itnout daily for millions of ppl.

    Use of pesticides and crops and spraying for mosquitos and fleas will also end up down there.

    Editors Note: It is clear that this commenter … ”Bawb” … is a troll.
    It is clear that “Bawb” has no formal scientific training in this area, and had done no formal research to document his false claims.

    In contrast, I am a professor of Water Quality, working professionally testing water since 1976.

    As a property owner in Yucatan since 1991, I have researched these facts carefully, and have seen over 30 yrs of scientific test results that confirm the report above … 3 decades of facts that refute this troll’s fake claims.
    Dr. Steven M. Fry

    • Rob says:

      So…. the big water tank on top of my roof needs regular cleaning, at least twice a year, and keep a lid on it to keep out the debris and critters. Test the tap water once or twice a year (using a pool test kit is fine) and if I want to do a deeper dive ( to look for pesticides, metals and other nasty chemicals ) then I need a more professional test kit. The water is HARD so be mindful and research any water purification systems, I may want to buy, that will not be damaged by the hard water build up. Does this sound about right Doc ?

      Rob N

  10. Margaret A Metcalf says:

    How do I find out how deep my well is?
    I live in Chicxulub Puerto. This article talks about Merida but title says Merida and Yucutan.
    Who can test my water in taps and tinnaco?
    My white towels are no longer white. Even when washed with bleach and vinegar.
    Difficulties with pool when I add water to it.

    Please help.

    • yucalandia says:

      Put a weight onto a long cord or long wire … and lower it into the well, until it touches bottom.

      For basic water quality, you want results for one of these fecal coliform tests:

      Análisis de agua – Enumeración de organismos coliformes totales,

      organismos coliformes fecales (termotolerantes) y escherichia coli – método del

      Determinación de Coliformes totales…


      are certified to analyze for coliformes fecales total. … Total Fecal Coliforms => poo bacteria,
      Cheers, Steve

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