Shipping Container Pool

The section drawing above shows the standard layout: the last ~1 m of the box is a filtration bay — pump, filter, optional heater and chlorinator behind a bulkhead — and the rest is water. That leaves a swim zone of about 4.8 m in a 20 ft container and about 11 m in a 40 ft, both a constant 2.35 m wide: a one-swimmer lane, sized like a short lap pool rather than a family free-form pool.

Depth is a design choice, not the full 2.39 m internal height. Builders typically set the floor or fill line for 1.2–1.5 m of water (most commonly ~1.35 m): deep enough to swim and stand, shallow enough to keep weight, bracing and safety manageable. Some models use the full-height end for a plunge section; true diving depth is not achievable in this format.

Volume is a straight multiplication of the wetted box. 20 ft: 4.8 m swim length × 2.35 m width × 1.35 m depth ≈ 15.2 m³ ≈ 15,000 litres; stretch the swim zone to 4.9 m and the depth to 1.5 m and you reach ≈ 17.3 m³, with generously sized designs touching 19,000 L. 40 ft: 11.0 × 2.35 × 1.35 ≈ 34.9 m³ ≈ 35,000 L, spanning ≈ 33,000–40,000 L across the 1.2–1.5 m depth range.

Those litres drive the running costs: heating 35,000 L by 10 °C takes ~407 kWh of delivered heat, and a 40 ft pool needs roughly twice the pump, filter and chemical throughput of a 20 ft. It is the strongest argument for the smaller box in cool climates — half the water heats twice as fast for the same heater.

Here is the number most brochures skip. Water is 1,000 kg/m³, so a filled 40 ft pool carries 33–40 tonnes of water — but the box’s maximum payload is 26,740 kg, and its corner-post structure assumes cargo resting on the floor, not fluid pressing on the walls. A filled 40 ft container pool exceeds the rating of the very container it is made from; even a 20 ft’s 15–19 t, while under its 28,250 kg payload on paper, is nothing a truck or crane will move as liquid cargo.

The consequence is universal: container pools are transported empty (5–10 t with structure and finishes — an ordinary crane lift, see moving a container) and filled on site. And since 20–45 t must then bear on the ground permanently, the pool sits on a reinforced concrete slab or engineered piers — ~200 mm of reinforced slab is typical; bare gravel is not enough. Base options and loads are covered in the foundation guide.

A container wall is ~1.6 mm corrugated sheet, engineered as a shear web for stacking loads in the wall’s own plane — not for pressure perpendicular to it. Water at 1.35 m depth pushes on the wall base at ~13.5 kPa, a distributed outward load the corrugations were never asked to carry; an unreinforced container filled with water visibly bows its side walls and works its welds.

Every serious conversion therefore welds a rib cage before the liner goes in: vertical steel sections (typically 50–100 mm box profile) tied between bottom and top rails at ~0.5–1 m spacing, often with a stiffened top rim that doubles as the coping. Then comes waterproofing — a welded reinforced-PVC or fibreglass liner, or an epoxy-coated fully welded steel tank inside the box. When comparing quotes, ask specifically what reinforcement and liner system is included: it is the difference between the $16,500 pool and the $30,000 one, and the thing that fails if omitted.

Above-ground is the format’s home turf: the box sits on its slab, the 1.35 m wall becomes a built-in safety barrier, plumbing stays accessible, and many designs glaze one wall as a window. Access is by stairs and a small deck. It is also fully reversible — the pool cranes out as easily as it arrived, which matters for rentals and resale.

In-ground installation buries the same box in an excavation: visually a conventional pool at conventional excavation cost, plus two engineering notes — external corrosion protection (bitumen coating and drainage against soil moisture) and groundwater management, since an empty steel tank in wet ground wants to float. Semi-recessed — sunk 0.5–0.7 m with a deck at coping height — splits the difference and keeps the filtration bay serviceable.

US installed prices, 2025–26: factory-built 20 ft container pools run $16,500–28,000 and 40 ft units $25,000–40,000, delivered and craned onto a prepared base; the slab adds $2,000–6,000 and site electrics $1,000–3,000. Heaters, covers and glazed windows are the common extras. A DIY build from a used box ($1,200–2,500 for the 20 ft shell) can halve the cash cost in exchange for the welding, lining and plumbing labour.

A comparable in-ground gunite pool runs $50,000–100,000+ and takes months of siteworks; fibreglass shells land between at $35,000–65,000. The container pool’s case is speed (swimming within days of delivery), a small-footprint lap shape, and relocatability. Its limits are just as clear: a fixed 2.35 m width, a lane rather than a lagoon, and steel that must be maintained like steel.

A pool holding more than ~19,000 L (5,000 gal) — or in most US jurisdictions, anything deeper than 600 mm — needs a building permit plus barrier compliance: a 1.2 m (4 ft) barrier with self-latching gates, which an above-ground container’s own walls often satisfy where a ladder-removal or gated-stair detail is used. Electrical work must meet NEC Article 680 — bonding of the steel shell is not optional in a pool that is steel — and some areas add setback and drainage rules. Budget 2–8 weeks for approval before the crane date.