Natural Swimming Pools: Step by Step How to Build Guide

Curious about natural swimming pools? Thinking about building one in your backyard? We did it, with the help of a contractor. In Mexico. And I’m here to tell you all about it.

Designing natural swimming pools (or natural swimming ponds) is the latest trend in green living. They’ve been very popular in Europe for some time but only in the last decade or so the trend has hit North America. And when I did the research for another story here on Fresh Patio that featured natural swimming pools, I made up my mind. One day, I wanted a natural pool. (The Koi pond story worked nicely into the narrative – very cool Koi towers.) I figured I should learn how to build a natural pool. Even though I wouldn’t be hands on, I still needed to understand the process.

As it happened, we were about to purchase a house in Cuernavaca, Mexico – one that had no pool. Part of the ‘buying a house in Mexico plan’ included a pool – or a price with enough room to build one. So now we needed to install a pool (this city has more swimming pools per capita than anywhere in the world except Beverly Hills). Was this synchronicity? Maybe.

Natural Swimming pools

Why Choose a Natural Swimming Pool?

You might wonder why people are choosing natural swimming pools over other types. We’ve had a saltwater pool (up north) and loved it. But the truth is, the salt is turned into natural chlorine in a saltwater pool, so there still is chlorine in the water (albeit much better for your skin than a conventional pool). And then there’s the Ion system, which is less chemicals but you still need chlorine. Much less is required than a standard pool, but you’re still swimming in chemicals.

Plants clean natural swimming pools

With natural swimming pools, all of the filtration is done by the aquatic plants. It’s a longer process. Once natural swimming pools are built, it takes at least a month before the ‘ecosystem’ establishes itself and the water gets crystal clear. You do nothing once it is established. Nature takes care of your pool maintenance. It’s organic. Think of that freshwater lake that you swam in as a child. Crystal clear, right?

How Much Does a Natural Swimming Pool Cost?

And I’m sure your next question is going to be “How much does it cost to build natural swimming pools?” And of course, it depends on the size and configuration. And your location. Do you want a cement bottom or are you happy with a plastic bottom? How large do you want the pool? Do you want heat? What’s your source? Solar? Gas? Electric heat? Will your pool be totally separate from the regeneration zone? Or will they flow into each other? And remember, the regeneration zone (water garden) needs to be at least the same size as the swimming zone. It’s better if it’s bigger. All important questions. And clearly, the first step is designing your natural swimming pool. There’s no accurate budget until then. In general, you can build a natural swimming pool in the US for anywhere from $30,000 to $100,000 and up. And of course, here in Mexico, it is less expensive. Wait until you hear how much less.

Turn a boring yard into a natural swimming pool

This was our lawn and one garden wall when we bought the house. Those topiary bushes are Bougambilia –  purple, not really flowering and ugly as sin. And lots of grass to water – and mow. So our first design decision – where to put the pool – was clear. Get rid of that lawn. And those round topiaries.

Palm trees

So, we had them removed and added some palms, bananas and other tropicals. After all, there’s no point in living in a tropical climate  if you don’t do tropical plants. At least not for my money. It’s actually a very Mediterranean climate in Cuernavaca. But technically, we are: Tropical savanna climate, mitigated by elevation. We sit at about 6,000 ft above sea level. We hired a separate garden person to design and plant the tropical wall. Because our natural swimming pool person is the expert in water gardens, not land gardens.

Big palm trees

They just kept bringing in plants. We gave the designer a (modest) budget and the trees kept coming. We wanted the surroundings of our natural swimming pool to be tropical and we weren’t disappointed.

Tropical wall

The tropical wall was complete before we started digging out the pool. Poor palms could use some water in this photo.

How to Design Your Natural Swimming Pool

The design really does determine the cost. We knew we wanted a large swimming lane. The designer/contractor we chose had lots of experience and had built some pretty incredible looking natural swimming pools. We were ready. First came the blueprints from the architect (who was a sub-contractor).

natural swimming pool

Here are the plans for the natural swimming pool. Canal de nado is ‘swimming channel’ and plantas acuaticas is ‘aquatic plants’. Our contractor spoke English as well as his native Spanish, or the process would have been more difficult. Measurements in Mexico (and most countries in the world) are in meters. In feet, the total pool is 40ft x 25ft with the swimming canal being 40ft x 10 ft. That’s room for two of us to do laps at the same time. Lots of room. In total, 1,000 sf with 400 sf being swimming zone.

Swimming channel

The solar heating for the swimming canal will be on the roof of the casita (bottom right). The house is not shown, but begins at the bottom left. A ‘casita’ is the northern equivalent of a bunk house or sleeping cabin. Sometimes, they call it a ‘bungalow’ here in Mexico when it doesn’t have a kitchen.

Layout for natural swimming pool

Cross section plans showing decorative plants, aquatic plants, the circulation system and stairs. The swimming channel is 10 ft x 40 ft (3 meters x 12 meters).

Natural Swimming Pool Construction

Bulldozer arrives

Time to call in the big guns to dig out the natural swimming pool.

What have we done?

They started to dig up the ground. It was a real OMG moment. Then, they hit rock. Solid rock. They had to use a hydraulic hammer attachment and could only do so much. I think that was after they hit our waterline. Which they fixed.

The hole gets deeper

He got a lot of it done but then they had to bring in three guys who hand chipped and formed the excavation area into the proper shape to pour cement. That took a month. It was excruciating to watch them. At this point, we were wondering if this building a natural swimming pool idea was going to work out.

Building the Concrete Floor and Walls

Building the pool

First it was rebar – then insulation to retain the heat in the pool. And then  two plywood walls that they would fill with cement.

Building the wall

It was a long process – the front yard would look like this for months. Being Mexico, when we were promised completion in three months, we knew that would never happen. It took a lot longer. They can finish a regular cement pool in three weeks. But natural swimming pools? Not so much.

It's a huge job

They poured cement between the two plywood walls, which encased the rebar.

Cement walls going up

This is the swimming channel. The rest of the pool is just dirt right now – that will be the plant regeneration zone.

The walls are amazingly straight

The regeneration zone has a cement floor now (left side.)

Curved cement walls

Now, to build a curved cement wall for the plant regeneration zone. This is a big job! Bigger than we thought. A lot of work goes into natural swimming pools (despite how natural they look). A cement pool would seem easy in comparison. Now, that is. Will it be worth it? We sure hope so.

Cement walls

Getting there! Unfortunately, the Bismark palm, the big beautiful silver one in the middle of the tropical wall, didn’t have a big enough root ball and it died. But they were guaranteed, so the garden designers will replace it but not until the rains come. They paint the interior of many natural swimming pools black, to better mimic a natural pond –  and to retain heat.

I like to swim in warm water, especially first thing in the morning. I can’t imagine anything more peaceful than swimming laps toward an infinity edge and a 200 ft canyon – at dawn. Well, I swam in my friends’ infinity pool on the beach at dawn and that was pretty awesome too (and pretty warm).

Lava Rock is a Natural for a Natural Swimming Pool

Decorative edging volcanic rock

The exterior walls are edged in lava rock, to match the house. This took an extra month. Originally, we thought the pool would be built to grade. But not so. The land tilts too much. Maybe they might have noticed that when designing? One thing you need to learn in Mexico is patience. Two things. Patience, and flexibility!

Lava rock exterior

These pipes will be part of the solar heating system. The actual pipes will be underground once complete.

Lava rock - infinity edge

All of this was done by hand. Even breaking up the larger volcanic rocks to the right size. This is the infinity end of the pool. Boy, the yard is one big mess.

Casita to the back right

We can see it starting to look like a pool. The concrete pool is ready. Now hurry up, already! We want to swim. Little did we know, this is just the beginning…now we need to create an ecological zone…

Stairs into the pool

The stairs look great. The remaining grass, as you probably notice on the right, is dry. This is dry season (October – May).

Main house in the bakcground

That is the house in the rear – and the Birds of Paradise flower garden. Beyond that are Bougainvillea against the far wall. Once it starts to rain, they will explode in color (photo below). The great thing about Cuernavaca, like many Tropical savanna climates, it rains primarily at night during the rainy season. Occasionally in the late evening. But mostly once we are in bed.

Painting a Natural Swimming Pool

Building a natural swimming pool

The Jacaranda in the distance (the purple tree on the right) gives away the season – they usually bloom in March/April. Sometimes earlier. This year, it was March. And the pool bottom painting is almost complete. It’s black to help retain heat, and to keep it looking more like a natural pond. Each stage seems to take forever at this point but it does have to dry. Have you ever watched paint dry? We’re starting to wonder about the wisdom of taking on a project this large.

Jacarandas off the infinity edge

Another angle – and more Jacarandas.

Black bottom retains heat

One last strip to paint black, but they ran out of paint. And it’s a custom color, so we waited another week to cover that little patch of green. The regeneration zone also has a layer of fabric beneath the paint.

Setting up the Water Garden and Regeneration Zone

Rock base for water plants

Now, they’ve put what they call “substrate” into the regeneration zone (looks like rocks to me). There was a layer of fabric under the black paint in the regeneration zone as well.  And we’ve slowly started to fill the swimming channel, on the advice of the contractor. Big mistake.

Filling the pool

He wanted us to start to fill it so that the water would get warm bit by bit (it’s a huge amount of water) and so that the plants could start to establish an ecosystem, bit by bit. But things got delayed, and the water just sat there – and got green and mosquitoes started breeding. Not good.

How to Combat Mosquitoes

Natural swimming pools need moving water. They had *planned* to get the water circulating through the filters, but you know how it goes (took them another three weeks). And the water just sat there. You think someone experienced in this stuff would know better but one thing we’ve discovered in Mexico (well, in life) is that you better know stuff yourself. Because in the end, it’s not their problem, it’s yours. So I googled: ‘Natural Swimming Pools Mosquito Control’. And this is what I found:

Mosquito Dunks

Organic Mosquito Dunks – and I had them delivered (we have Amazon Mexico and a great site, Mercado Libre, which is like eBay). A natural solution and easy to use and they solved the problem in a few days. Harmless to fish and plants. Highly recommended. And we bought two large water pumps and put one at each end to circulate the water.

Fish in the Natural Swimming Pool

The pool is getting filled

The plants actually belong on the other side. We also got two koi, who eat the mosquito larvae. And then we got about 100 mosquito eating fish (they look like guppies) and they are in there too. I guess it’s all part of building the ecosystem. Some people might get squeamish about swimming with fish, but they’ll live in the regeneration zone. The two large macetas (pots) you see on the left are the housing for the charcoal filters and will be spill over pots. By the time that the ecosystem is established, we won’t need those mosquito dunks anymore.

Filling Your Natural Swimming Pool

Keep the water circulating

The pool will fill to the top, (another 30 or 40,000 litres easily) and the plants (and fish) will move to the left. It takes a long time to fill a pool this size. It’s most important that the water be crystal clear. Which we’ve accomplished with other large water garden ponds, so we aren’t too worried. Yet. LOL.

Here Come the Water Garden Plants!

Building the water garden

Now, we are finally getting the water plants in the correct side of the pond, with many more to come. Papyrus, Horsetail, Bullrush (cat tails we used to call them up north) – and then of course, lotus and water lilies.

It got a little murky

We slowly filled in the water. It took a great deal of water.

Great pond plants

It looked murky at first. The filters are in the large urn/pots – charcoal and filter material, and they’ll spill over the tops of the pots.

It was a process to fill the natural swimming pool

Slowly, it fills in… and starts to clear up somewhat, even without the filters being operational yet.

Pond plants filter the water

Starting to look natural

The plants are free floating in the swimming channel portion of the natural swimming pool to clean the water while its ecosystem adapts. There is a lot of water in the swimming channel, as it is much deeper. You won’t be swimming in them, they will be relocated to the regeneration zone on the left side.

Charcoal filters inside the terra cotta pots

Finally, our natural swimming pool is full and the filter pots are working, with the water slowly spilling over their lips, after passing through the charcoal and filters.

Swimming channel is great

There are far more plants at the moment than there will be at the end. We used lane floats to make a barrier so they would stay on the ‘regeneration zone’ side.

It looks like a lake

The infinity edge dips off the end…

Natural swimming pool

The solar heat is still to come and we need to attach the swim channel floats in a more permanent fashion but it’s coming along! My husband is swimming already, but I’m waiting for it to get warmer (it’s about 26C right now, or about 78F, just with the sun alone). We’re starting to like the look, however. And can’t imagine a normal swimming pool in its place. This looks so incredibly natural. I guess that’s the point.

the other view

The Long View

There will be far fewer plants in the regeneration zone of once the system is established – the regeneration zone will look more like a water garden/koi pond. We really like the black bottom and how it reflects the vegetation. You’ll see it’s now the rainy season – the grass is green again. Nine months and counting. And I bet there are two months left before the solar is in and everything is adapted and self-sustaining.

water garden plants

Many of the plants will be removed from the water garden portion of natural swimming pools as they adapt. They just need a lot of plants in the beginning to establish the natural filtration system. And our large terra cotta pot filters spill over gently and look amazing.

Love the tropical wall and lava rock

Things are getting a lot greener now that the evening/nighttime rains have arrived. The natural swimming pool is really starting to blend into the surroundings. Still waiting for the solar heat to be engineered (all the pipes are in place).

The Bougainvillea against the far wall have started to bloom.

The deck at the casita end of our natural swimming pool is almost done – you’l see the spot for the solar pump, it will be in a metal case in the ground.

natural swimming pool

It really does look wonderful – even though it’s taking a very long time. We’re quite happy with the end result so far. If you have any questions at all, please just leave them in the comments, I’ll be happy to answer. I’ll keep updating as the solar system is installed.

tropical wall and natural pool

Cost of Building Natural Swimming Pools

I know, we told you we would let you know the cost. The basic calculation is that if you want an in-ground cement natural swimming pool, it will cost you the same as a regular in-ground cement pool with pool decks and landscaping. The difference is, you need to build something twice as large (at least) as your swimming zone. The costs run about $100 per square foot. I won’t make you do the math – this pool would have cost in the $100,000 range to build in the USA. In Mexico, in US dollars, it worked out to about $25,000. And we never have to fill it (just top it up occasionally) and never have to add anything to the water. That is so refreshing.

And for $25,000 we got:

  • a cement/concrete lap pool (40 ft long x 10 ft wide) at 400 SF
  • the entire regeneration zone (also concrete with fabric) at 600 SF 
  • water garden / regeneration zone (with real lava stone facade and pond filters)
  • solar heating system on the casita roof

It's all about the view in this natural swimming pool

Questions? Just ask us – we are happy to respond to your queries. And as noted, I will keep updating the photos as the natural swimming pool builds its own ecosystem and establishes itself. There should be far fewer plants in the regeneration zone, eventually, and we will add more koi to turn it into a more of a water garden look. And for sure, I am getting one of those koi elevators.

About Beverley Wood 45 Articles
Beverley Wood is a freelance writer and communications consultant living in Mexico City - WhiteDogCreative.com