Most people will use their polytunnel to rear tender plants and largely, to grow their own food. But polytunnels can also be used for more frivolous purposes. For example, you could use a polytunnel to cover a sustainable, eco-friendly natural swimming pool, to make it more useable in the UK climate (and to provide some privacy from neighbours).
A natural swimming pool is one which uses only natural methods of filtration (gravel, plants, beneficial fauna) to keep it clean and fresh without the addition of any nasty chemicals. These pools can offer a more organic and relaxing place to enjoy a swim. They are cheaper to create than ordinary back garden swimming pools and will, unlike most pools, cost nothing at all to upkeep and run.
At least 50% of the pool area should be devoted to the reeds, sedges and other aquatic plants that will act as a natural filter for the pool's water. A rim located just below the surface of the water between the swimming and plant zones allows water to pass over for filtering but keeps separation between the two. A simple aquarium pump will keep the water moving and prevent it from becoming stagnant and this pump can be run using solar or wind power.
Once established, all a natural swimming pool will need is the occasional management of aquatic plants and a little tidying up here and there and it can stay fresh, cool and clean for years to come. A polytunnel protecting it from the elements and blown leaves and debris will make it even easier to manage and will allow you to use it for much more of the year than you would be able to if it were open to the elements.
A swimming pool is always going to be a little frivolous and something of a luxury. But with a natural swimming pool there will also be benefits to the local wildlife to a degree, and what is more, you will be doing no damage to the planet or to the local environment. All of that can help you to rest easier as you enjoy luxuriating in your own private natural pool.
If you use your imagination, you could even create a hanging garden above your natural pool, to grow some herbs, salads or other plants at the same time as enjoying the space for recreation. Polytunnels really can and do offer great value for money – there is just so much that you can do with them.