Gert Wingårdh, in a car from Gothenburg to Malmö, 10 September 2019. Look! There it is! [Nods out the side window] Shouldn't we go and have a look at the building site? Would love to! [Parks next to a crane lorry] Careful where you tread. We should've had a torch. It's Stonehenge! Fun, isn't it, with this enormous scale? It's extraterrestrial!

Stonehenge was nothing we considered when designing it, but I've noticed it's a recurring reference — though Stonehenge is only a third of the size.

It doesn't look like a water tower… A traditional water tower is a reservoir that's filled and emptied like a toilet — sometimes the water is still, sometimes emptied, sometimes refilled. But this is a full-flow tower, filled and emptied continuously. The water should never be still; it should swirl, move, oxygenate.

It swirls round? Exactly. And then the ring-formed cistern is perfect: you send in water and after one turn you empty the cistern.

Doesn't that mean you need two cisterns? That's what we have here, placed outside each other, layer upon layer, in a circle. It was Jonas Edblad who got me to see the cisterns as two rings — the sudden realisation that these ring tanks could be arranged as planets in orbit. Saturn outside Jupiter, Mars outside Earth. The site at the hub of the ring I imagine can be used for weddings and parties.

Joakim Lyth and Gustaf Wennerberg, co-workers, Malmö office, 30 September 2019. We tested two alternatives, 90 and 150 metres in diameter, but the municipality preferred the 90-metre one. NCC Infrastructure are building it; they normally build roads and bridges, so Gert's demands were daunting at first. But Gert told them, "Cast it however you want! This design is so strong it will survive anything!" Liberating.