From water head to request
What is water head in a drain flow rating?
Water head is the depth of water standing above the drain while its flow is measured. Viega states the drainage capacity of its model 4967.10 at an accumulation height of 10 mm and of 20 mm, each marked in accordance with EN 1253.
The makers cited here use different words for this condition.
| Term on the data sheet | Used by |
|---|---|
| Head of water | QuARTz by ACO; Infinity Drain |
| Accumulation height | Viega; Kaldewei |
| Build up | ACO Building Drainage |
| Water level according to norm | Dallmer |
How much does standing water change the figure?
On one maker’s table the same drain’s figure is about 78% higher at 15 mm than with no standing water. The steps read QuARTz by ACO’s flow table for its ShowerChannel; they are not a rule for other drains.
- No standing water (0 mm): the channel body alone is listed at 0.41 l/s.
- At 5 mm head of water the same body is listed at 0.60 l/s.
- At 15 mm head of water the same body is listed at 0.73 l/s.
- With the Wave grate fitted: 0.38, 0.54 and 0.66 l/s at the same heads.
ACO USA’s installation guide lists its own ShowerChannel body in GPM: 6.65, 9.51 and 11.60 at 0.00, 0.20 and 0.60 in of accumulation.
At what water head do makers rate their drains?
The makers cited here state figures at 0, 5, 10, 15 or 20 mm, or at 1/2 in.
| Product | Head stated | Maker’s figure |
|---|---|---|
| QuARTz by ACO ShowerChannel, body only | 0, 5 and 15 mm | 0.41, 0.60 and 0.73 l/s |
| ACO Building Drainage ShowerDrain S+ floor drain, Stripes, 50 mm trap | 10 and 20 mm | 0.7 and 0.8 l/s |
| Viega model 4967.10 | 10 and 20 mm | 0.45 and 0.6–0.75 l/s |
| Kaldewei FlowDrain Horizontal Regular | 20 mm | 0.8 l/s |
| Dallmer CeraLine Plan F 500 mm | 20 mm (norm water level) | 0.70 l/s |
| Infinity Drain listed figures | 1/2 in | GPM, by product |
Dallmer prints the norm’s minimum flow rate, 0.80 l/s, beside the product’s own capacity. A figure stated at 20 mm should not be set against one stated at 5 mm.
Do the grate and the trap change the rating?
They can, on ACO’s tables. ACO USA says adding a grate throttles the intake of water into the channel body. QuARTz by ACO lists most ShowerChannel grates below the body-only figure, and its Linéaire grate at the same 0.60 l/s at 5 mm.
| Configuration | Maker’s figure |
|---|---|
| QuARTz by ACO ShowerChannel at 5 mm, body only | 0.60 l/s |
| Same channel, Wave grate | 0.54 l/s |
| ACO Building Drainage ShowerDrain S+ floor drain at 20 mm, Stripes, 50 mm trap | 0.8 l/s |
| Same drain, Stripes, 30 mm trap | 0.6 l/s |
| Kaldewei FlowDrain Horizontal Regular, DN50, 50 mm sealing water | 0.8 l/s at 20 mm |
| Kaldewei FlowDrain Horizontal Flat, DN40, 30 mm sealing water | 0.63 l/s “with a required 20 mm” |
For its ShowerPoint at 5 mm, QuARTz by ACO lists from 0.6 l/s (Quadrato grate) to 1.1 l/s (Wave grate). A rating belongs to one body with one grate and one trap.
Which standards sit behind drain flow ratings?
The European makers cited here refer to EN 1253; ASME and CSA Group list two standards that cover shower drains. Only catalogue scope and makers’ statements are given:
BS EN 1253-1:2015
BSI lists it as current and under review. It covers floor gullies inside buildings with a trap water seal of at least 50 mm.
DIN EN 1253 as makers cite it
Kaldewei calls 0.8 l/s at 20 mm a standardised drainage capacity under DIN EN 1253. Dallmer prints 0.80 l/s and 20 mm as the norm’s minimum flow rate and water level.
Water seal
TECE says DIN EN 1253 requires odour traps to have a sealing water height of at least 50 mm. Dallmer marks the 30 mm water seal of its product as deviating from DIN EN 1253.
ASME and CSA standards
ASME lists A112.6.3/CSA B79.3 (2022) for floor drains; shower-area drains of outlet NPS-2 and smaller are covered there and in A112.18.2/CSA B125.2, which CSA Group lists in its 2020 edition, reaffirmed 2025.
- Standard and edition cited
- Water head of the figure
- Water seal depth
Does the product rating predict the installed result?
No. QuARTz by ACO says pipework design may restrict the flow further. Three things sit outside the product figure:
Waste line and venting
Infinity Drain says most US residential installations use a 2 in waste line with an average capacity of 9 GPM at 1/2 in head of water, assuming proper venting.
Outlet size
QuARTz by ACO says AS/NZS 3500 requires at least a DN40 connection for showers and calls DN50 the common industry standard. ACO USA’s guide, dated February 2022, says ASME A112.6.3-2001 requires a 2 in outlet for showers. ASME now lists a 2022 edition, and the installed outlet size comes from the plumbing code adopted locally.
Position in the shower
QuARTz by ACO gives up to 0.42 l/s for a channel at the entrance with no water accumulation, and up to 0.6 l/s against the wall with a 5 mm head.
A test water head is a measuring condition. Treat the acceptable depth of water on the floor as a separate project requirement.
How much water does the shower send to the drain?
That depends on every outlet that can run at once, not on one showerhead label. Watch the units: drains above are listed in l/s or GPM, showerheads in gpm or l/min.
| Source | What it states |
|---|---|
| EPA WaterSense | Standard showerheads use 2.5 gpm; labeled showerheads no more than 2.0 gpm. |
| WaterSense specification, version 1.1 | Maximum 2.0 gpm (7.6 L/min); body sprays are excluded. |
| TECE | Gives 10–15 l/min as the flow of average shower heads. |
| Infinity Drain | Asks whether there are multiple shower valves. |
How should a buyer compare drain flow ratings?
Line up the conditions first, then the numbers. This is procurement guidance, not hydraulic design.
- Add up the shower. List every outlet that can run together.
- Get the head. Ask at what water head each figure was measured.
- Name the rated assembly. Body, grate, trap depth and outlet size.
- Match the conditions. Mark offers at different heads as not comparable.
- Align the units. Convert l/s, l/min and GPM first.
- Involve the designer. Pipework and acceptable floor depth are theirs.
When the grate or outlet changes
If the grate, trap or outlet changes after selection, ask whether the earlier rating still applies. Keep the rating with the accepted configuration. If the conditions cannot be supplied, mark capacity as unverified.
What should you send and ask before a quotation?
Describe the shower and ask for the rating with its conditions.
| Question | Why it matters |
|---|---|
| What is the flow figure, and in which unit? | Makers list l/s or GPM. |
| At what water head was it measured? | Heads cited here run from 0 to 20 mm. |
| With which grate? | QuARTz by ACO lists 0.54 to 0.60 l/s at 5 mm, by grate. |
| With which trap and water seal depth? | ACO Building Drainage lists less with a 30 mm trap. |
| With which outlet size? | The waste line can limit the flow. |
| Which standard is cited? | EN 1253 or an ASME/CSA standard. |
Include with your request
- Shower outlets and their flows
- Drain type, length and position
- Grate and outlet size
- Waste line size
- Project location and quantity
WNS Global confirms any offered drain, its documents and commercial terms separately in writing. This guide does not state that WNS Global drains have any flow rating, water seal depth, test or listing named above.
