The garden, which aims to show people how they can help solve local flooding through gardening, won a Gold Award and Best Show Garden award at the RHS Hampton Court Flower Show, which runs this week.
Instead of pouring down drains, the water filters through gravel beds, runs down channels into flowerbeds, through permeable paving, into a pond and soakaway hollows, and feeds and nurtures a variety of marsh plants that help to keep the water clean.
Most of the plants used (see below) are British natives. Summer flowering plants have been selected for colour including loosestrife, flowering rush and greater spearwort – providing a predominant purple mixed with cream and yellow.
Several features are recycled. The pagoda roof is the inverted roof of a grain silo; bench supports are made from the curved girders from the same silo; the cascade was an air duct from a warehouse; the chain cascade is made from the chains of an old harrow; old sheets of metal have been intricately carved to make relief water scenes of dragonflies and kingfishers.
The garden pavilion is built on a wooden platform weighing six tonnes, which spreads the weight of the structure across the Hampton Court ground underneath.
Cairns has created the garden with WWT so that it can be transported to WWT's Washington Wetland Centre when the show is over, to become a permanent outdoor classroom as part of HSBC's Water Programme.
Judges said they found the garden "really easy to judge". They liked the story behind the garden; they appreciated how delicate many of the wildflowers were to transport and plant; and they loved how Cairns had juxtaposed one of the wildest-feeling gardens at the show with some creative use of recycled industrial materials to recycle water.
Cairns said she was "amazed and delighted" at the accolades.
"The garden demonstrates it's relatively easy for anyone to recycle water by getting creative with recycled objects. It's more difficult to do this for a show where you're using mature native plants that are so fragile and can easily snap, but it was worth it because the effect is beautiful. I'm really pleased that all the hard work crafting metal and wood and making the water system work has been recognised.
"It's all about spreading the message that water is important and you can use it creatively rather than waste it."
THE FULL PLANTING LIST
Alisma plantago aquaticum
Caltha palustris alba
Hydrocharis morsus ranae
Ranunculus lingua grandiflorus