The constraint that shaped everything
A dry-deck splash plaza is not a fountain with children near it. It is a public bathing facility that happens to have no basin, and the water has to leave the nozzle at drinking-water quality, because a four-year-old will stand over a jet with their mouth open. That single fact sets the plant room, the plant room sets the budget, and the budget sets how many jets you get.
The treatment train
Full turnover in 43 minutes on a 12 m³ working volume: 25 µm pre-filter, medium-rate sand, medium-pressure UV at 40 mJ/cm², and a free chlorine residual held between 0.5 and 1.0 mg/l by an amperometric controller with a second, independent sensor that can shut the plaza down on its own authority. The tank is stainless, not concrete, so it can actually be inspected. Every one of those choices is more expensive than the ornamental equivalent and none of them is optional.
What we gave up to pay for it
The competition scheme had 180 jets on individual valves. We built 129 on 22 zones. Nobody has ever noticed, because a child cannot see a valve; what they respond to is whether the pattern is unpredictable. Nine programmes on a randomised sequencer, with the two tallest zones locked out above 30 °C ambient so the plaza does not become an unshaded 3.6 m wall of water in a heat event.
Operating cost, stated plainly
Around 74,000 kWh and 1,900 m³ of water a year over a 210-day season, plus a weekly two-hour service visit. We put that number in the tender return. Two of the four bidders did not, and the Trust asked them why.
