A concrete shed with a full water filtration system, including a pump, three tall blue cylinders, a grey garbage bin, a dark grey hot water heater, a long horizontal UV light and green plumbing joining everything together.

Making Clean Water in Yucatán

Jake Robins - Personal

An oft-discussed adjustment anyone moving to Mexico from a place like Canada eventually has to make is figuring out the water situation. When we first arrived here in 2021 we lived in Mérida for about a year and didn't think too deeply about it because we had good water pressure and it was easy enough to just buy bottled water to drink and focus on the countless other things we had to figure out as brand new immigrants. In late 2022, however, we bought a home in a small town outside the city, and with the move to a less developed neighbourhood, I started to think about water a lot.

In Yucatán, there are generally four deficiencies in the municipal water supply that need to be addressed in order to elevate our water service to the standards we were used to in Canada.

  1. The water is not potable.
  2. The water is heavily mineralized (hard water).
  3. The water is not pressurized.
  4. The water is not available at all times.

Let me walk you through the system we have in place to address all four of these deficiencies.

The Yucatecan Water Supply

It's probably helpful to talk a little about where our water comes from. Hang in here while we do a little bit of geology. The entire Yucatán peninsula is a large limestone slab and forms what is called a karstic system. Limestone is a soluble rock; over time, as water passes over it, it dissolves, creating pores and gaps in the bedrock. This process creates a system of underground caves, sinkholes, and the well-known cenotes that bring tourists here year after year. Rain water is absorbed very quickly into the ground through these pores, which is why we have very few rivers or lakes in this area. It also means we have a tremendous ground water supply.

Mérida sources most of its water from three large wells outside of the city and the supply is supplemented by smaller wells inside the periférico (Mérida's outer ring highway) as well as private wells on individual properties. Our small town north of the city has its own municipal well and a water tower to provide water for the surrounding homes.

A map of Mérida sourced from Google Maps. To the southwest, south and east are three markers indicating the locations of the primary water supply wells for the city. Google
Mérida's primary water supplies

This aquifer has a few inherent weaknesses that are worth noting. First, Yucatán does not have a very thick topsoil layer on top of the karst. Soil acts as a natural filter for pollutants, which means the Yucatecan water supply is at high risk of contamination from surface pollutants from agriculture and industry. Second, Mérida lacks a centralized wastewater treatment system. Almost exclusively, wastewater is processed in situ by a septic tank on the property before being sent directly back into the aquifer. Some neighbourhoods have community septic tanks for an additional filter process, but ultimately, the stuff we put in the toilet ends up going straight back down into the ground below us, and I suspect that the quality of septic tanks across the region varies greatly.

Broadly speaking, the environment can handle the current human presence and our effects on the aquifer. A paper from 2015 by Rojas Fabro et al measured nitrate levels across Mérida's water supply and found that while 11% of samples exceeded maximum limits allowed by the World Health Organization for drinking water (mostly from the inter-urban supplies around central and northwest Mérida), there was "no health hazard of nitrates for adults" and that the "aquifer feeding the water treatment works in the periphery of the city (Merida I, II and III), does not pose mayor [sic] public health risks due to the presence of nitrates".

However, this system depends entirely on rainfall to dilute contaminants. There is no active work to clean it. The paper notes that this process is "highly vulnerable to long term due to unpredictable changes induced by climate change scenarios and current unsustainable socio-economic development in the region". In other words, if Yucatán continues to grow at its rapid pace and climate change gets worse, we could be in for some trouble. And what it means for individuals is that we can't really depend on the groundwater to be clean at any given point in time or at any given place in the region.

This unreliability cascades to another layer of challenges when it comes to clean water in Yucatán. Because the municipal supply is not considered potable, there is no reason to invest in water infrastructure that keeps it potable on the way to you. Pipes, cisterns, tinacos and other storage and transfer components between the groundwater and your tap are not cleaned regularly, and many people do not keep up with maintenance of rooftop tinacos or their own residential pipes. On our house, many of our pipes are exposed on the roof to the hot sun. It creates opportunities for bacteria to grow and multiply inside our pipes, even after the city has delivered us water. Many homes (ours included) opt for inexpensive PVC to carry water and is not designed with any kind of cleanliness in mind. We don't benefit from the anti-bacterial properties of copper here like we do back home. When we first started working on our home water system by installing a pressure pump, a huge amount of green algae started blasting out of our taps and showers, organic goop that had been growing happily in the warm, low-flow environment of our plumbing. It wouldn't have mattered if the city was shipping us Dasani right out of the bottle.

Four old cut white PVC pipes, with a thin layer of green algae visible inside the pipes.
The pipes we replaced, with visible algae growing inside.

I mentioned earlier that the porous nature of Yucatecan bedrock was a result of dissolving limestone. That dissolved rock doesn't just disappear. We have some of the hardest water I've ever experienced here. I had difficulty finding measurements to express this. I eventually found this paper which conducted an experiment at a small community in Campeche to install a solar still in order to soften water. The measurements from their wells and a nearby river registered 1,785 mg/L of calcium carbonate in 2021 and as high as 3,500 for this particular study. To put that number in to context, the Canadian government classifies "soft water" as less than 60 mg/L and anything over 180 mg/L as "very hard". Mexico defines a maximum hardness of 500 mg/L to be fit for human consumption. I had heard that drinking very hard water may lead to increased chances of kidney stones over time, but in doing research for this post I haven't been able to find actual evidence of that. Some studies even suggest hard water has positive health effects. I don't know how many of these studies examined water hardness of Yucatecan scale however.

Regardless of any health benefits or detriments, the hard water creates all kinds of other issues. Taps, faucets and toilets develop a scale build up that reduces their performance. We had to regular soak our shower head in vinegar overnight in order to keep the water flowing through it. This scale can seriously damage appliances, from your hot water tank to your coffee maker. Dishwashers are almost non-existent here, and the hard water is a contributor that. It's tough on your skin and hair, creating dryness and itchiness, and it fades my clothes after repeated wash cycles.

Lastly, a small note about availability and pressure. Our local water tower provides minimal pressure via gravity to the house, but this is all we get. The system is not itself pressurized via any kind of pump system. It's also not sending us water consistently, like you would expect in Canada or the United States. Often, especially during the daytime, there is no water coming out of the tower to our home. In México, to work around both these issues, people install what's called a tinaco on their roof, which is essentially a personal water tower, a small reservoir that holds a family's supply of water that is available on demand. Typically, it fills up overnight while the local supply is serving. The rooftop location provides a small amount of gravity pressure as well. These tinacos are ubiquitous in Mexico; look across the rooflines of any neighbourhood and you'll see tons of these. Our home has two tinacos, each with 450L of capacity.

Two tinaco tanks on the flat roof of a house, one tank coloured tan and the other black. The Rotoplas brand name is visible on the tan tank,
Our Tinacos

So all told, we had some work to do.

The System

To help us with this setup, we contacted José Ramon Medina from Ecolife de México (also on Facebook). It's not my intention to make this a promotional post but the truth is he did a great job and we're really happy with the setup, so hopefully this recommendation is useful to someone else. What I liked most about our solution is that we were able to custom fit it to our particular home; it definitely isn't cookie-cutter. We had a lot of extra requirements that we were able to knock out in one big job, which was nice. He also speaks great English, which is something I try not to limit myself to while working with local contractors but is of course really nice when it works out.

My general plan was to create a "pipeline" of processes that started at our tinacos and would output clean, soft water, both hot and cold. Before installing this there was some really funky plumbing set up that routed water back and forth across the property in order to go around construction features and get to the hot water tank and back. It was a disorganized mess, a patchwork of pipes that had been upgraded and iterated on a number of times in a pretty shoddy fashion. The hot water tank was at ground level in our yard, outside, and was suffering from environmental damage. We took the opportunity to redo this plumbing, replace our hot water heater, and consolidate our little water assembly line on the roof, where we had some available space to house it all. In order to protect the system from the sun and the rain, José Ramon brought in some albaniles (masons) to build a utility shed around everything. As with everything here, it's built out of cinderblocks, even the roof.

A small, cinder block utility shed being constructed on a flat roof.
The new utility shed, under construction.
Workers installing the roof to the water utility shed, suspending cinderblocks across the wall and a crossbeam.
The albaniles installing the shed roof.
A concrete utility shed, recently constructed, with plaster finish.
The utility shed after plaster finish.

The back of the shed faces south and takes the brunt of the sun at any given time of day, for most of the year. Once the install was done, we also added an aluminum sliding door to the front.

With the shed complete, José Ramon got to work installing the individual pieces of the new system. I think it's probably easiest to just lead with the whole photo, and I'll go through the pipeline step by step to explain what's happening. Hover over the steps to get a label, and click to see the full explanation.

A concrete shed with a full water filtration system, including a pump, three tall blue cylinders, a grey garbage bin, a dark grey hot water heater, a long horizontal UV light and green plumbing joining everything together.
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The water filtration system

Pump

The first step in the pipeline is to pressurize the system. This small Truper 0.75HP water pump is equipped with a pressurization sensor. It sucks water out of the tinacos and pressurizes the system after it. You set a max and minimum pressure value on its gauge. As you use water, the pressure drops. Once it falls below the minimum value, it kicks on to push it back up again until its reaches the maximum value. It runs continuously while taking a shower or refilling a toilet tank, but is otherwise off. We actually installed this pump last year (it's a relatively inexpensive upgrade) and were able to re-integrate it in to the new system. One day when this pump dies I may replace it with one that is somewhat quieter, but it doesn't bother us too much as it is.

There is an option to add a pressure vessel storage tank after the pump. This basically adds more volume to the pressurized part of the system, which means that small consumption like washing your hands or rinsing a glass won't withdraw enough water to drop the pressure below the minimum level. That reduces wear and tear on your pump since it will start and stop fewer times (though it runs longer when it does come on). It can be pretty expensive and most people opt not to do it since it probably ends up cheaper to just replace your pump over and over again. We followed this advice.

Sediment Filter

This filter removes macro-sized things from the water, such as sand, dust, leaves, debris, and other larger pieces. I haven't seen a whole lot of this kind of debris in the tinacos or in our own well water, but it's a good safety to protect the rest of the filters should anything get through the municipal system into ours.

Both filters and the water softener are housed in Purikor fibreglass tanks.

Three blue coloured fibreglass tanks, tall and skinny, with black valves on top and an input and output pipe.
Purikor Fibreglass Tanks

Carbon Filter

Our carbon filter is a granulated activated carbon (GAC) filter. These have been around for a very long time and are a great first defence against unwanted water contaminants. They are particular adept at removing organic chemicals from water. Some things that you might expect it to remove include fuels like gasoline or diesel, solvents, pesticides and herbicides, bleach, & chlorine. Given what we talked about regarding groundwater intrusion from agriculture and industry, I'm thankful to have this as part of the system. I joke that it is the filter that removes the frog pee from the water. It also does a good job of getting the taste of water to a more neutral place.

The way activated carbon works is pretty cool. The carbon itself is really porous (like the karst!) which gives it a high surface area to weight ratio. This maximizes the amount of water that comes in contact with the carbon as it passes through. The ratios on activated carbon can be as high as 2000 square metres per gram! That's like wrapping an entire olympic-sized hockey arena over a single gram of carbon and having every part be in contact with it. This is an exercise in spatial comprehension that I can't really wrap my head around (ha!).

Water Softener

The water softener works using a process called ion exchange. The water is passed through a reservoir of resin beads charged with a sodium ion. They are negatively charged anions. Calcium and magnesium (the two main contributors to water's hardness) are positively charged, and so they are attracted to these beads, getting pulled out of the water as it passes through.

As part of the softener's maintenance, it requires a special brine tank. You'll see it next to the blue tank - a grey, garbage-bin looking thing. Inside this is a concentrated brine solution, water filled with specially made salt pellets. If you backwash the filter with the brine, it will do the ion exchange process in reverse, attracting the calcium and magnesium away as it flushes through. More about this process in the maintenance section.

A view into a grey coloured plastic tank, half full with grape-sized salt pellets.
Brine tank with specially made salt pellets

Ultraviolet Light

Our softened, decontaminated water can still present danger in the form of viruses and bacteria, the truly nasty stuff that you do not want to get caught drinking. The final step of the main filtration system passes the water underneath an ultraviolet light which illuminates the water at a specific wavelength chosen for its ability to damage DNA. This essentially "kills" living organisms, or at least prevents them from replicating, which eliminates the threat of water-borne diseases. E.coli, cholera, algae, dysentery, and hepatitis B are all things that get stopped at this stage of the system. It's more effective than just a chlorine treatment.

A shiny metallic UV light, long and skinny, mounted horizontally on the wall of the utility shed. Water flows in one end and out the other from green pipes. A small rectangular electrical box has a digital readout that says 365.
Ultraviolet Light filter, with digital readout for replacement schedule

Pipes and Infrastructure

I mentioned how existing plumbing was often not setup to protect clean water in Yucatán. Our home was no exception and when we bought this house the rooftop was setup as a grid of cheap PVC pipes sending water from the tinacos to the bathrooms and kitchen. It wouldn't make a ton of sense to spend all this money and effort to clean the water only to send it back into these dirty, algae-filled pipes. So as part of our project, we pulled out as many of these as we could and replaced them with something better.

a bundle of several green coloured PPR pipes on a gravel driveway.
PPR (Polypropylene Random Copolymer) pipes

These are Polypropylene Random Copolymer pipes, known as PPR pipes. It's a fancy kind of plastic, really, but well-suited for food-grade water use cases. It was developed in Germany and operates at a wide temperature range, is corrosion-resistant, and is real slick on the inside, promoting good flow. Compared to PVC which is joined using PVC cement, PPR is joined with a heat gun, essentially melting the pieces together. This prevents any kind of chemical leaching into the water supply. We used a product called Turboplus from Rotoplas, which has two specific additional benefits we were after. The insides have an anti-bacterial coating to prevent any more of that goop from developing, and the outsides have a UV protection coating which will help preserve the integrity of the pipes when exposed to the Yucatecan sun.

The only pipes we couldn't replace were the ones that were in the walls themselves. Essentially, our roof is the "circuit board" of the plumbing, but when the pipe reaches the right room, it drops down into the wall to feed the showers, taps, toilets, etc. We didn't feel like breaking open our concrete walls and making a huge mess and incurring a huge cost. But these pipes were just as dirty as the ones we replaced, so we had to do something.

To get around this, José Ramon cut them open and performed a thorough cleaning, filling up the pipes with a series of acid and bleach washes, letting them soak while he installed the rest of the system. After this was done, we flushed them really well to clear out any remaining guck and we were good to go. Since these pipes are in the walls they are at least protected from the sun.

Reverse Osmosis

The system described above gets you about 95% of the way there to potable water. The water that comes out of the main system is well-suited for showering, toilets, appliances, etc. We wash our dishes with it and brush our teeth with it. If you drank it, you would probably be fine, but for a little extra confidence, we have one final step in the pipeline: a reverse-osmosis system. This component is installed under the sink in our kitchen, and feeds a separate, second faucet specifically for drinking water. This system has some similar components with the main system - another carbon filter, another UV light, etc. I like to think of it as a "second pass" that does polishing work on the water quality.

A small plastic all-in-one device with three cylinders standing vertically underneath. On top, a fourth cylinder lays horizontally. Behind it, a shiny UV lightbulb sits. Electrical wires and plumbing lines weave around it.
Final reverse-osmosis filter beneath out kitchen sink

The product we have is an all-in-one unit from Purikor that plugs into the wall and receives your main cold water line as an input. It is considered five-step. First, the water passes through another sediment filter, another activated carbon filter, and then a block carbon filter. The block filter is similar to the granular carbon, but made of even finer pieces, meaning it is even more effective at removing contaminants.

From here, the water is pushed through a semi-permeable membrane, the key component of a reverse-osmosis system. This process removes almost all the dissolved solids in the water, but comes at a cost of "wasting" about half the water you push in. The clean half continues on through the system while the "dirty" half is discarded directly into the sink's drain. Following this, the final two steps (another carbon filter for polishing and a final UV light for sterilization) creates clean, odourless and flavourless drinking water, which is sent to a small faucet above.

Two kitchen faucets. A regular one on the right, brushed nickel with a single valve. A smaller shiny one on the left with a small valve.
Don't talk to me or my son ever again

The reverse osmosis system has some drawbacks. It takes a bit to kick in once you turn the tap on - it has its own little pump and has to spin up to a certain flow rate before you get water out. In addition, both the carbon block and the membrane itself have a pretty noticeable effect on flow rate, which means that filling up water bottles or pots of water for cooking takes a little bit of time. This is why we maintain a separate tap for non-drinking purposes, with full pressure and flow rate.

A small shiny kitchen faucet outputting water. The flow rate is small and the stream is fine.
Small flow rate from the drinking faucet

Maintenance

A system like this requires some maintenance. Some of it requires my attention, most of it is automated. Here's a rough breakdown of the steps we go through to keep it running in tip top shape.

Filter cleaning

The sediment filter and carbon filter both require regular cleaning to dispose of the contaminants that they pull out of the water. Thankfully, this is as easy as backwashing the filters (running water through them in the opposite direction). The filter products we use have mechanical timers on them that automatically do this every 3 or 4 days or so. It basically pumps water through them for about 10-20 minutes, which is then ditched out a drain into the garden. The backwash plumbing is separate from the main plumbing so it's all pre-done and requires basically none of my attention.

Softener Regeneration

Much like the filters, the water softener requires regular backwashing as well, but instead of plain water it uses the concentrated brine in the brine tank. Thankfully, it's automated as well, so I don't have to think too much about this. The pellets self-regulate to keep the brine concentration correct, and the system refills it with water as needed.

The salt pellets mentioned above need to be refilled periodically, however. The more you use the system, the more brine flushing is required, and each flush uses up some of the salt. Generally, I check on this once per month, but in practice I only end up adding a bag of salt pellets every 5 weeks or so since we don't have heavy water use. The bags are 20kg and cost approximately $300 MXN (around $24 CAD or $19 USD at the time of this writing). We can just buy them at Home Depot or at our pool supply store, Jose Barroso. The only not very fun part is hauling it up a ladder to the roof, but let's be honest, I can use the exercise.

UV Light Bulbs

The ultraviolet light bulb needs replacements every year. The system comes with a handy digital clock which counts down the days for you. You just slide them out and pop the new one in. I haven't replaced one yet obviously, but a quick search tells me they are on the order of $500 MXN (about $41 CAD or $30 USD).

Reverse Osmosis System

All the filters on the reverse osmosis system are replaceable as well. I haven't had to replace anything yet, 3 months after install. The volume going through it is very small, and all the water that comes to it has already gone through the main system, so it's considered to have a light load. Purikor says the filters need to be replaced every 6-12 months. They sell an entire maintenance kit for the all-in-one unit, including filters and UV bulb, for $750 MXN on Amazon (about $62 CAD or $45 USD).

Tinaco Cleaning

Since the water now passes through four different carbon filters, we give the whole system a little bit of a head start on cleaning by adding a half litre of bleach to each of the tinacos about twice per month. The chlorine keeps anything from growing in the tinacos, which are not air-tight or pressurized, and the filters remove the chlorine before it reaches the taps. Let me tell you that it takes a fair amount of trust to actively pour bleach into the water that you eventually drink. But carbon filters excel at removing chlorine, and knowing that there are four of them between the bleach and my mouth, we got comfortable with it in soon enough. This bleach is just regular household bleach you can get at the supermarket, and runs us around $60 MXN per month ($5 CAD or $4 USD) in costs.

It's also good practice to have your tinacos emptied and scrubbed clean every six months or so.

Costs

The big question after all this is "how much did all of this cost?" Of course, each home is going to have unique needs so the figures here may not completely line up with a solution for your own house here in Yucatán. I've omitted our costs for the extra plumbing work that we did as well as building the utility shed, since those were sort of special to us. But for the sake of transparency I'm happy to break down the key figures of the filtration system itself for you. The prices include the 16% IVA (sales tax). The CAD and USD figures are based on exchange rates from April, 2024.

I would also add that while these are the prices I received in early 2024, I can't guarantee how long they stay this way. In Mexico prices can fluctuate pretty dramatically, because a lot of these components are imported and the currency has been pretty volatile lately. If you're serious about doing this for yourself here in Yucatán, make sure to get your own quote that's relevant in your moment!

Water Filtration System Primary Costs
Item$ MXN$ CAD$ USD
Water Pump & Pressure Sensor$ 3,100$ 256$ 188
Sediment Filter$ 13,746$ 1,135$ 835
Carbon Filter$ 15,341$ 1,267$ 932
Water Softener$ 19,140$ 1,580$ 1,163
UV Filter$ 4,930$ 407$ 299
Reverse Osmosis$ 8,236$ 680$ 500
Filtration System Materials$ 3,770$ 311$ 229
Filtration System Labour$ 7,250$ 598$ 440

Obviously, this is a bit expensive, especially when you add in the additional work we did, but this system should be in place and last us for many years, perhaps even decades, so I try to ensure the cost is amortized in my head when I am evaluating its value. We only pay about $20 CDN per year for our municipal water service, so when comparing it to costs back home, it probably pays for itself within ten or fifteen years. I think our last water bill in Canada was on the order of $700 CDN per year. Many homes pay more.

I also feel really good about the grid independence achieved here, too. I haven't mentioned it much above, but we have our own well that serves as a backup water source and is piped into the tinacos, so we would actually be fine if the municipal water service disappeared entirely. Coupled with our solar panels, we can theoretically procure and clean our own drinking water without any government services at all. I'm not a "prepper" by any means but I do live in a developing country, and we're on a real albeit infrequent hurricane path looking down a future defined by climate change. So the extra confidence is certainly welcome. The older I get the more I kind of enjoy being independent and taking care of my own stuff in my own way.

All in all, this was a really fun project and doing it taught me a lot about water, which sounds like a funny thing to say but of course is really important. It certainly makes me appreciate the level of service we enjoy in our home country, and makes me realize how much we took it for granted. We're privileged enough to be able to afford this kind of system at our own home but many people are not. Access to clean drinking water remains a key challenge for over 40% of the world, and I worry about how much climate change will exacerbate this. I'm thankful I don't have to worry about that, and if there ever is some kind of emergency, it's nice to know we'll be able to help get ourselves through it, and maybe a few of our neighbours too.