Natural pool update

We dug the natural pool in August last year, so that we could use the clay to build the house.  It is coming along nicely:



We made a sundeck out of local chestnut this spring, but it’s been to hot to sit out there.  We’ve had no rain for over six weeks and the water level goes down a couple of centimetres every day due to evaporation.  We are having to top the pool up every few days from the well.  We’re opening up the old well in the barn this week, to use for the garden and the pool, but we really need some rain now.

FINAL UPDATE 2019: after three years the pool dried up in the summer.  It’s full in winter, when we don’t need it and dry in summer when we’d like to use it.  We can’t fill it from our well, so it is now a wildlife pond.  LESSON: If you are going to build a natural pool, make sure you have a sufficient water supply to fill it in the summer!

DIY Natural Swimming Pool

Building a cob house gave us the perfect opportunity to make a natural swimming pool.

We did as much research as we could before digging the hole, but we’re finding that there’s always something different about what we want to do and we can never find information that’s directly applicable to our situation.  This is what happens when you move out of the city.  Natural landscape has its unique characteristics that you have to work with.

Our land is clay, which is great for a cob house and pretty good for a pool.  We bought the Organic Pools Manual, which was the best information we found.  However, this was written for the UK and advised the use of a rubber liner, as this keeps the water a bit warmer.  It gets hot here in the summer, not as hot as southern Spain, but hotter than the UK for a longer period. Plus we have dogs.  There is no way we will be able to keep dogs out of the pool and a dog nail can easily make a hole in a rubber liner, as we found in our pond in London.

We decided to use bentonite clay to line the pool, which we bought from Absoal in Almeria.  They provided a really good service and delivered it all the way down our track, which is unusual.  We usually have to get deliveries outside the local cemetery. However, getting the bentonite around the pool was a real challenge.  It did not dig in easily like in any of the videos we saw and it was really difficult to get it to stick to the sloping sides of the pool.  We had to mix it with clay and put it on like mortar.  In the end we used less than half of the bentonite we bought and had to bale out and pump out the pool twice before we could finish it – it hasn’t had any problem holding water so far.

Initially we made the pool about 10 by 5 metres.  It’s essential for a natural pool to have a regeneration zone at least the same size as the swimming area.  So the swimming area was going to be 10 by 2 metres and the regeneration zone 10 by 3 metres.  Luckily, our first attempt didn’t work out because we didn’t get the levels right.  Our land is sloping and we ended up with a 2 metre deep hole, that would only ever have one metre of water in the bottom because the level at the other end was so much lower.  In order to bank up the sides where the land sloped away too much we had to dig a much bigger hole.  The pool is now about 20 by 12 metres, with a 20 by 5 metre swimming zone and it looks so much better.

We used large rocks from the old house to separate the regeneration zone from the swimming zone.  Once the pool is full the rocks will be about 50cm below the surface of the water.  That seems to be lower than what’s recommended elsewhere, but we’ll have to see if that makes any significant difference.  We had hoped to get another layer of slightly smaller rocks on the regeneration pool side, to make sure that any gaps between the larger rocks are filled to minimize soil and plant matter getting into the swimming zone.  We didn’t get time to do that before it rained, so we might be filling gaps in the summer.  The bottom of the regeneration pool has a good layer of bentonite and on top of that a layer of stones in varying sizes.  We have stones everywhere and it’s quite therapeutic to pick a bucket of stones from the food forest and throw them in the pool.

The pool is in a sheltered spot and will get sun most of the day.  There are some tall trees along the far edge that provide a little shade in the hottest part of the day to create some change in the water temperature and help the circulation.  We followed the advice in the Organic Pool Manual and have gone for an aerator rather than a pump and filter.  We needed a solar aerator as we can’t get electricity out to the pool easily.  There doesn’t seem to be much choice around.  Most solar air pumps seem to be for ponds and are too small.  At the other end of the scale the systems available were way out of our budget.  We settled on a Thomas Solar aerator, which is languishing in Spanish Customs as I write this.

We couldn’t find anywhere in Spain to get marginal plants to  clear the water at a reasonable price.  We need a lot of them because of the size of the pool and because it is so sunny.  We’re not too bothered if the water doesn’t get crystal clear, but we don’t want to be swimming in algae and we don’t want it to be a breeding ground for mosquitoes.  We found a company in Germany that sells aquatic plants for ponds and they were reasonably priced and super helpful. It’s not ideal to put in the plants when the pond is full, but we’re not going to pump it out again, so Dean has bought some waders.  I’m looking forward to seeing him in those!