A spray ground is the only surface on a park site that runs a storm on a timer, all summer, with two hundred barefoot children standing on the drainage. Here is how we capture that water at the perimeter — and where our catalog stops and your aquatic contractor's begins.
Zero depth, all day: what a spray ground asks of a slab
Splash pads spread for a reason that has nothing to do with drainage: no standing water means no drowning depth and, in most jurisdictions, no lifeguard line item. So we quote perimeter drainage for municipal park pads, YMCA wet decks, HOA amenity areas, school spray zones, campground play areas, waterpark zero-depth entries, and civic interactive fountains. What makes the slab unusual is that the water is deliberate: a pool holds its water, a spray ground throws its water and expects the site to carry it away all season. And the pad is dead flat or crowned at 1% to 2% — you cannot ask a running four-year-old to negotiate a grade — so it all sheets to the edges with almost no head behind it.
Four things then decide nearly every product choice here. The traffic is barefoot, so grate opening and temperature become injury questions, not aesthetic ones. The pad is an accessible route, so ADA governs the openings whether or not anyone says so. The debris is strange — sunscreen, sand, and wet clippings blind a grate face faster than leaves. And the crew that inherits your decisions is two people with a truck and forty other assets.
Two water systems share that slab — only one of them is ours
Nearly every confused call we take has one root: two separate systems live on that concrete and people discuss them as one. The feature water system — surge tank or vault, pump, filtration, UV or chlorine feed, controller, nozzles, and the pad's own sump — recirculates or runs once to whatever connection the authority having jurisdiction requires. We sell none of it, and sand interceptors or oil separators are downstream and by others.
Site drainage is ours: the pad perimeter, deck and apron, bathhouse hardscape, shade-structure leaders, the service drive, and the pipe path to a legal discharge. The distinction is practical. A recirculating pad means our line sizes for rain plus overspray; a flow-through pad discharging through a site structure means we need the feature schedule's peak gpm, because one line may carry both. Getting that backwards is the most expensive mistake on the job.
The wet surround: french drains around a pad, and why they aren't ours
Walk any municipal splash pad and you will find subsurface drainage within thirty feet of the slab, because the wet surround is where aquatic sites actually fail. A french drain — perforated pipe bedded in washed stone, wrapped in geotextile — is the standard answer under the irrigated turf ring, under poured-in-place safety surfacing, and along shade-structure footings. It is worth doing and we do not sell it: that pipe, stone, and geotextile are contractor-installed, and nothing in our catalog is a french drain.
Where the two layers meet is the useful part. An underdrain moves water that has already infiltrated, slowly; pad discharge is fast, concentrated, on the surface, and it silts an underdrain closed in a season. So the pattern that works is a surface-collection layer at the hard-to-soft transition: a channel along the pad edge, a catch basin at the low point, and the underdrain tied into that same basin. One structure, one lid, both systems served.
Where the water goes, and how to put a number on it
Water leaves a splash pad the way water leaves a table: it runs to the edges and falls off. That puts the drainage at the perimeter, not in a scatter of inlets where children stand.
Find the low edges first. A crowned pad wants a full perimeter line; a pad pitched one way has a single downslope edge that takes nearly all of it. Then walk for where water concentrates off the slab — the turf transition, the corner where the walk meets the pad, the shade-structure downspouts. Each wants a basin rather than a hope.
Put numbers on it. One inch of rain on 1,000 sq ft of impervious surface is about 623 gallons, so a 2,500 sq ft pad sheds roughly 1,558 gallons per inch. Volume tells you what the site absorbs; peak flow sizes the pipe. Run Q = C × i × A with C near 0.95 for finished concrete, and that 0.057-acre pad under a 4 in./hr design storm produces about 0.22 cfs, or 98 gpm. Our Runoff Calculator does the arithmetic and Sizing for Storms shows the method; feature flow comes off the schedule and nowhere else.
Then check the outlet, the bottleneck nine times out of ten. Running full at 1% in smooth pipe, Manning's puts a 4 in. line near 100 gpm, a 6 in. near 300, an 8 in. near 640 — so a 90 ft run ending in one 4 in. outlet is a 100 gpm system no matter how much channel is in it. Compare grate intake figures only at matching head, and pitch buried pipe 1/8 in. to 1/4 in. per foot so it stays self-scouring.
Half an inch: the rule that governs every barefoot grate
Take one specification off this page and take this one. Section 302.3 of the 2010 ADA Standards states that openings in a walking surface must not pass a sphere more than 1/2 in. (13 mm) in diameter, with elongated openings run perpendicular to the dominant direction of travel. A splash pad is an accessible route, so it governs every grate in it — see Understanding the ADA.
Now tighten it, because 302.3 was written for wheelchair casters and cane tips, not a six-year-old's toes at a dead run. Inside the play envelope there is no dominant direction of travel, so the orientation half of the rule protects nobody and round-hole perforated patterns beat bar slots. The mistake we see most often is trusting an ADA checkbox instead of the opening dimension, which moves a long way inside one brand: the Spee-D grate opens 3/8 in. × 3-1/4 in., the 18 in. basin grate 7/16 in., the 5 in. Pro Series HDPE grate 1/2 in. × 1-1/4 in., the 8 in. 5/8 in. × 2 in. Compare patterns in the channel-grate catalog and the metal-grate section.
Barefoot-zone grate spec, by where you are standing
Load class needs its own line, because pedestrian areas on park sites almost never stay pedestrian. Class A 15 (15 kN, about 3,372 lbf) is right for a surface nothing drives on and wrong for nearly every perimeter we have walked, because the mower, the cart, and eventually a pickup all get there. Class B 125 (125 kN, about 28,100 lbf) is our floor anywhere a wheel can reach, C 250 covers service drives, D 400 a fire lane — full ladder in the Load Class Recommendation Guide.
Two material notes finish the picture. A foot registers heat flux, not temperature: cast iron conducts at roughly 50 W/m·K against about 0.45 for HDPE, so metal goes where the load class demands it and light-colored plastic where the children are. Then fasten every grate inside the play envelope — children pry, and a lifted grate is the worst failure mode on this list. Set grates 1/8 in. to 1/4 in. below finished surface so the concrete carries the wheel and nobody catches a toe on a proud frame.
Where each piece lands on an aquatic site
Channel at the pad perimeter is the main event and where the budget belongs, intercepting sheet flow before it reaches turf — the difference between a sod ring and a mud ring by mid-July. The failure we see most often is not an undersized channel; it is a correctly sized channel with one 4 in. end outlet 80 ft away and no basin at either end.
Catch basins go at low points, run ends, direction changes, and wherever the underdrain ties in. Sizes run 9 in., 12 in., 18 in., and 24 in., with kits, risers, and universal outlets for 3, 4, 6, and 8 in. pipe.
Everything else on the site. Where a spray ground shares a deck with a pool, cast-in Frontier Deck Drain and Flowmaster handle deck edges and coping — that is the pool deck drainage page. Bathhouse roof leaders dump concentrated flow where people queue, which a small basin and the right drainage fittings fix cheaply, and a rated-lid valve box over the isolation valves beats the callback.
Discharge, with a caveat we won't soften. Storm-side water can go to pop-up emitters, a dry well where soils and codes allow, or a storm connection where permitted. Treated feature water from a flow-through pad is a different substance to your AHJ, and many jurisdictions require sanitary — do not infiltrate it because the storm line was closer.
In stock · 4 ft and 10 ft sections · opening 3/8 in. × 3-1/4 in. · Class B
Our first pick for a neighborhood-park pad, an HOA amenity, or a school spray zone — and the reason is the grate, not the channel. That 3/8 in. opening sits well under the sphere limit, in six colors including sand, gray, and white, at 16.92 sq in. of open area per foot. The body holds about the volume of a 4 in. pipe, cuts with a miter saw, and has bottom flanges that stop it floating in the pour. Class B is the ceiling: if a truck crosses it, wrong channel.
In stock · 0–9° deflection per 8 in. section · 51 GPM · no couplings
Splash pads get drawn as circles, arcs, and kidney shapes far more often than rectangles, and a perimeter of straight sticks and mitered corners around a curve is ugly, slow, and leak-prone. Contour sections snap together with up to 9 degrees of deflection each and no couplings, so an arc or closed loop follows the pad edge instead of chasing it. Class B and 51 GPM — run Contour through the radius and straight Spee-D down the tangent.
In stock · 0.7% built-in slope · 48 in. sections · 3.998 in. to 12.062 in. inner depth
Past roughly 40 ft on a flat slab, pre-slope stops being a luxury: Dura-Slope molds 0.7% of fall into every 48 in. section, so a long run gains invert depth without anyone chasing grade with shims, and radius couplings turn bends as tight as a 30-degree radius. Channel and grates are tested to AASHTO M-306 and EN 1433 (DIN 19580) methods by an independent AASHTO-accredited lab — useful when a municipal spec wants evidence. The grate range is why we reach for it: plastic perforated in white and gray at Class B (8.75 sq in. open per foot, 26.77 gpm per foot at 1/2 in. head), stainless and galvanized perforated, and ductile iron on a rated frame at the crossing. Best of all is the galvanized Slot Top, published by NDS as meeting both ADA and heel-proof standards: no grate face to heat up, no pattern to catch a toe, nothing to pry. Plan its ends — NDS's detail puts 2 ft of slot top plus a 2 ft maintenance unit in the first and last four feet, and that unit can sit inside the catch basin.
In stock · 17-11/16 in. square × 18-9/16 in. deep · 2- and 4-opening bodies
The highest-return item on the job and the one most often value-engineered out. Every inch of sump below the outlet invert banks about 0.18 cu ft — roughly 1.35 gallons — so an outlet 6 in. off the floor gives about 8 gallons of quiet sump where sand drops out instead of migrating into the lateral. Four-opening bodies let one structure take the channel run, the underdrain, and a roof leader. Step to 24 in. at the site low point, 12 in. at isolated corners.
In stock · 101.75 GPM per foot on the 5 in. grate · iron grate options
Where the mower, the cart, and the occasional parks pickup cross the line, the product changes even though the pad does not. The 5 in. Pro Series carries 23.52 sq in. of open area and 101.75 GPM per foot at Class B, with eight outlet positions per section and iron grates where the class climbs. The 8 in. Pro Series steps up at a delivery apron — but its HDPE grate opens 5/8 in. × 2 in., wider than the sphere rule allows underfoot, so keep it at the crossing rather than over-building the whole perimeter.
Quote-only · K100 4 in. internal / 5.12 in. overall · Class E, Class F on PowerDrain
When an engineer's spec names polymer concrete, a cast-in edge rail, or a specific EN 1433 class, this is the line. K100 sections are one-meter modules of polyester polymer concrete — 14,000 psi compressive, 0.07% water absorption, frost and salt proof — with a galvanized edge rail cast in and 0.5% built-in slope running up to 131 ft 3 in. of continuously falling trench. For aquatic work the grate catalog is the draw: perforated galvanized and stainless grates published as ADA types, QuickLok versions for fast removal, and heel-resistant Brickslot slot-tops with access sections. MiniKlassik K50 does the same at a smaller footprint, K200 and K300 pick up where a plaza collects more than a pad, and PowerDrain adds a ductile iron edge rail up to Class F. ABT, EJ, US Foundry, and the Josam Pro-Plus line are quotable on request. ACO is priced per project rather than sold from the cart — send run length, load class, and grate type and we will quote it within one business day.
In stock · order the grate SKU, the exact color, and the screws together
Grates on aquatic sites go missing, crack under a mower deck, get pried by a determined eight-year-old, and get discontinued in a color three years after the pad opens. Buy 10% to 15% of your linear footage as spares at install — exact SKU, exact color, with a box of the flat-head #8 × 1 in. stainless screws those grates take. A crew swapping a grate in ten minutes on a Saturday is the difference between a coned-off section and a closed pad on the hottest weekend of the year.
Opening day, mid-season, closing day
Season opening. Pull the perimeter grates and shop-vac the basins before the water goes on — whatever blew in over winter is in the sump you paid for, and emptying it is one person for an hour.
Mid-season, once. A July pass with a hose and a stiff brush over the grate faces keeps intake capacity where you designed it.
Closing. Vac the basins, verify the outlet runs free, check every grate screw, and replace what is missing off the spare shelf now — not in April with a ribbon-cutting booked.
What grate opening is actually safe for bare feet on a splash pad?
Start at the ADA rule, then go tighter. Section 302.3 of the 2010 ADA Standards says an opening in a walking surface must not pass a sphere more than 1/2 in. in diameter, with elongated openings placed perpendicular to the dominant direction of travel. Read the opening dimension off the sheet every time, because it moves by grate and not by brand: the NDS Spee-D channel grate opens 3/8 in. × 3-1/4 in., the 18 in. catch basin grate 7/16 in., and the 8 in. Pro Series HDPE grate 5/8 in. × 2 in. Inside a play envelope children run every direction at once, so slot orientation protects nobody and round-hole perforated patterns beat bar slots.
What load class should I spec around a splash pad?
The play surface is pedestrian — EN 1433 Class A 15, 15 kN or about 3,372 lbf — but almost no park site stays pedestrian, so anywhere a mower deck, a utility cart, or a pickup can reach the line we make Class B 125 the floor: 125 kN, about 28,100 lbf. Service drives go to Class C 250 (250 kN, about 56,200 lbf) and a fire lane to Class D 400 (400 kN, about 89,900 lbf). NDS Class A at 3,372 lb per foot and Class B at 28,100 lb per foot are those same EN test loads in pounds, so the scales line up. H-20 as a 16,000-lb wheel and HS-25 as 20,000 lb are AASHTO heuristics, not an EN equivalence.
How much drainage capacity does a splash pad need?
Two loads, and they add only where they share a line. One inch of rain on 1,000 sq ft of impervious surface is about 623 gallons, so a 2,500 sq ft pad sheds roughly 1,558 gallons per inch; run Q = C × i × A with C near 0.95 for concrete and that 0.057-acre pad under a 4 in./hr storm produces about 0.22 cfs, or 98 gpm. Take feature flow off the water-feature schedule; nozzle counts vary far too much to guess. Then check the outlet, the bottleneck nine times out of ten — at 1% in smooth pipe, Manning's puts a 4 in. line near 100 gpm, a 6 in. near 300, an 8 in. near 640.
Does Drainage Connect sell splash pad recirculation, filtration, or pump equipment?
No. We sell collection and conveyance only — channel, grates, catch basins, fittings, valve boxes, and the pipe path off the site. Surge tanks, pumps, filters, UV and chlorine feed, nozzles, controllers, and the pad's own sump belong to your aquatic contractor, governed by your state pool code and the Model Aquatic Health Code language many states apply to interactive water play venues. Sand interceptors and oil separators are downstream and by others. We will spec the site drainage around all of it, and we will not quote any of it.
How do we keep sand and sunscreen from silting up the line?
Give the grit somewhere to drop out before it reaches the pipe. An NDS 18 in. catch basin body measures 17-11/16 in. square by 18-9/16 in. deep, so every inch of sump below the outlet invert banks about 0.18 cu ft — roughly 1.35 gallons — and an outlet 6 in. off the floor gives about 8 gallons of quiet sump. Put a basin at every run end and every change of direction. A shop vac on the basins at opening, mid-season, and closing then beats a jetter on a silted 4 in. lateral.
Speccing a spray ground or a wet deck?
Send the pad dimensions and pitch, whether it recirculates or drains to waste, the feature schedule's peak gpm, and what crosses the perimeter — we'll spec the collection side and quote it within one business day.
