Natural swimming pool inspired by David Pagan Butler: how the gravel bed and airlift system work, and how to adapt them at home

If you have looked into building your own natural swimming pool, you have probably come across David Pagan Butler's videos. This Briton, based in Norfolk, built his own chlorine-free swimming pools and then shared his method in widely viewed videos and a self-build guide. His approach is appealing because of its simplicity: a pool, a planted gravel area, drains, and a small air pump to circulate the water. Recreating a pool “like Butler” mainly means adopting his principle: purification through a continuously traversed planted gravel bed, driven by highly energy-efficient circulation, and then adapting it to your land, climate, and intended use. Here is how this system works, what it really requires, and what needs to be adjusted for it to deliver on its promises at your home.

Where the Butler method comes from

David Pagan Butler is neither a pool industry professional nor a design consultancy: he is a self-builder who sought to obtain clear swimming water without chemical disinfectants, using simple means. He built his own pools in his garden, filmed the stages, documented both his successes and his mistakes, and then published a self-build guide. His videos attracted a large audience, and many amateur projects across Europe now draw inspiration from them.

This success can be explained by one strong idea: rather than pumping the water to an external filter, it uses the soil in the planted area itself as the filter. The water flows through the gravel from top to bottom, is collected by drains at the bottom, and then returned to the swimming area. This is similar to planted downflow filtration, which professionals call a downflow filter, but carried out with very ordinary materials.

How it works, step by step

To understand the method, follow the path of a drop of water.

1. In the swimming area, the water is clear but contains particles, dissolved nutrients, pollen, and microorganisms brought in by the air, rain, and swimmers.
2. It passes through the regeneration zone, separated from the swimming area by a low wall or bank that reaches just below the surface.
3. It flows down through the gravel bed, where plant roots and a bacterial biofilm covering every grain live. Particles are retained, organic matter is decomposed, and some nutrients are absorbed.
4. It is collected at the bottom by perforated drains, laid on the liner beneath the gravel.
5. An airlift raises it: air injected at the base of a vertical pipe lightens the water column, which rises and overflows toward the swimming area. The water thus removed from beneath the gravel is replaced by water infiltrating from above.

The gravel is therefore not decoration: it is the pool's biological reactor, and the entire system depends on how consistently water passes through it. A weak but continuous flow, day and night, is better than a powerful flow for a few hours a day.

Airlift, or how to pump water with air

Airlift is an old technique used in aquaculture and aquariums. A vertical pipe is immersed in the water; at its base, an air pump injects a stream of bubbles. Since the mixture of air and water is lighter than water alone, the column rises and overflows at the top, provided the height to be overcome remains low. An airlift cannot raise water by one metre, but it circulates it very efficiently between two ponds that are almost at the same level.

Its advantages for a natural swimming pool are numerous. The air pump stays dry, out of the water, with no submerged electrical parts near swimmers. It consumes little power, around a few dozen watts for common models, compared with the hundreds of watts used by a conventional pool filtration pump. It oxygenates the water while moving it. Finally, there is neither a rotor that wears out nor a strainer that becomes clogged at the bottom of the pond.

Its limitations are just as clear: the flow rate depends on the pipe diameter, the injection depth, and the height to be overcome. For a large pond, several airlifts are needed, or the air can be combined with a low-consumption water pump. To find out when a water pump becomes preferable, see our article which pump for a natural swimming pool.

Butler method or technical natural swimming pool: what changes

No approach is inherently superior. The Butler method is remarkably simple, but it requires space and does not tolerate shortcuts well. A more technical natural swimming pool is more forgiving and takes up less land. Many successful projects lie somewhere between the two: a generous planted gravel bed, aerated by airlifts, with a skimmer for floating debris.

Design points to pay attention to

The surface area and depth of the gravel zone

In a low-tech system, the planted surface does the work. Plan for a regeneration zone roughly comparable in size to the swimming area. A gravel layer a few dozen centimeters thick, placed above the drains, provides enough volume for the biofilm and roots while remaining easy to pass through.

Choosing the gravel

Use washed gravel, free of fines and soil, with a uniform particle size so that water circulates everywhere. Avoid materials that release limestone or undesirable elements, and above all any substrate containing potting soil or fertilizer. Phosphorus is the number one enemy of a natural swimming pool: it directly feeds algae. Some self-builders use volcanic rocks for their high porosity; the principle remains the same.

Drains

Lay the perforated drainage pipes in a regular network across the entire surface, connected to a manifold that supplies one or more airlifts. A single drain in the middle of a large area drains only its immediate surroundings: the rest of the gravel stagnates and eventually operates without oxygen. Also provide access for flushing the drains, as they become clogged over the years.

Waterproofing

Some projects rely on compacted clay soil. In practice, on most sites in our regions, an EPDM or PVC membrane remains the safest way to retain water and prevent the surrounding soil from supplying nutrients. Protect it with geotextile felt underneath, against stones and roots, and above in the gravel area, against punctures.

Plants: choose species that do the work

In the gravel bed, plants play three roles: they absorb some of the nutrients, their roots aerate the substrate and provide support for the biofilm, and their foliage shades the shallow water. Prioritize native or well-acclimatized aquatic and semi-aquatic species that can tolerate having their roots in poor gravel: yellow flag iris, water mint, purple loosestrife, marsh marigold, rushes, as well as submerged oxygenating plants in the shallow swimming area.

Plant bare-root plants, rinsed clean and without any potting soil around the roots. Absolutely avoid invasive exotic species covered by European regulations, even if they are still offered here and there. For a detailed selection, see our article which aquatic plants to choose for your natural swimming pool, or our guide to downflow or upflow constructed wetlands.

Adapting the method to Belgium and northern France

Norfolk's climate is not very different from that of our regions: wet winters and increasingly hot summers in spells. The method therefore adapts well, with a few nuances.

• Heat waves are the critical period: the water warms up, oxygen levels drop, and algae growth accelerates. A sufficiently deep swimming area and some shade over the regeneration area help cushion these peaks.
• In winter, the air pump can continue running to maintain some circulation and an opening in the ice, but the bubble must remain far from the bottom of the swimming area if animals overwinter there.
• Autumn leaves are the main source of phosphorus: a net stretched over the pond for a few weeks can prevent years of imbalance.
• Formalities: depending on your municipality and the size of the project, a permit or declaration may be required. Find out before you start digging.

Filling the pond and the first season

Once the pond is filled, the gravel bed is sterile: it takes several weeks for the biofilm to become established, and longer if the water is cool. During this period, an algae bloom is common. This is normal, and it is precisely when you should not empty the pond, add any chemicals, or stop the circulation.

1. Fill it with water as low in phosphorus as possible. Have it tested if you use well water or rainwater that has been stored for a long time.
2. Start the airlifts immediately, continuously.
3. Seed the gravel with bacteria specific to natural swimming pools, following the manufacturer's instructions.
4. Plant in spring, when vegetation starts growing, so the plants can quickly take over.
5. Remove filamentous algae with a net as they appear: each handful removed takes nutrients with it.

Allow a full season for the system as a whole to find its rhythm. In the following years, the water generally stabilizes more quickly in spring.

The most common mistakes made by DIY builders

• A gravel zone that is too small compared with the swimming area, to save space: this is the number one cause of green water in summer.
• Unwashed gravel: fine particles clog the bed, water can no longer pass through it, and the bottom becomes anaerobic.
• Soil or potting compost in the planted zone or on the banks: a source of phosphorus for years.
• A single drain for a large area: most of the gravel is not doing any work.
• An airlift that is too high to overcome: the flow rate collapses. Keep the levels between zones almost identical.
• Turn off the pump at night to save energy: the biofilm lacks oxygen, even though the air pump already uses very little power.
• Panic at the first sign of greening and add an algaecide: you kill what was supposed to purify the water.

Maintenance over the years

A Butler-style pool requires little intervention, but it must be regular. In spring, cut back the dry plants and vacuum the sludge deposited at the bottom of the swimming area. In summer, remove filamentous algae and monitor the water level, topping it up with nutrient-poor water. In autumn, protect the pool from leaves and trim the plants before their above-ground parts fall back into the water.

Every few years, the drains should be rinsed, and a small portion of the gravel, the most clogged part, can be removed, washed and put back in place. This takes a few hours and extends the life of the system for a long time. The air pump simply requires periodic replacement of its diaphragms, wear parts specified by the manufacturer.

Also read

For the complete process of building a pool: How to build your own natural or ecological pool.

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Frequently asked questions

— Who is David Pagan Butler?

A British self-builder based in Norfolk who built his own natural swimming pools and shared his method through widely viewed videos and a guide entitled Natural Swimming Pools: A Guide to Designing and Building Your Own, published by Permanent Publications.

— Is an air pump really enough to circulate water in a natural swimming pool?

Yes, provided you use airlift circulation with suitably sized pipes and small differences in elevation. The flow obtained is modest but continuous, and this regularity is what matters for a planted filter. For a large pool, use multiple airlifts or combine them with an energy-efficient water pump.

— Can a Butler pool be built without a liner?

It can be considered on very clayey, well-compacted soil, but the risk of leaks and soil infiltration is real. For durable swimming, a waterproof membrane protected by geotextile remains the safest solution.

— How large should the planted gravel zone be?

With a system this low-tech, the regeneration zone must be generous: as a rule of thumb, an area comparable to that of the swimming zone. The smaller it is, the more fragile water quality becomes in summer.

In summary

• The Butler method: a planted gravel bed, drains at the bottom, and continuous circulation powered by an air pump.
• Pool water is drawn through the gravel, where biofilm and plants purify it.
• Electricity consumption is very low, but the regeneration zone must be large.
• Washed gravel, low in fines and soluble limestone, and a substrate without potting soil.
• A liner protected by geotextile secures watertightness in most types of soil.
• The first season is an establishment phase: be patient and use no chemicals.

Last updated: October 3, 2026.