The Dialysis Clinic and the Pressure Budget
A 24-station outpatient dialysis clinic will occupy the ground floor of a leased three-story building. Static pressure at the meter is 62 psi and the highest fixture is 38 feet above grade. Design flow through the 2-inch meter is 90 gpm. The water supplier's ordinance classifies dialysis as a high hazard, requires containment at the meter, and permits isolation assemblies inside the building only if the containment device matches the highest hazard on the premises. The contractor's plan shows a 2-inch double check valve assembly at the meter and a 1-inch reduced pressure principle assembly on the reverse-osmosis feed. The contractor argues the double check is 'already there' and that an RPZ at the meter will 'eat the pressure on the top floor.'
1. Can the double check stay at the meter? Address the containment-versus-isolation logic, not just the hazard label.
Read the worked answer
No. The ordinance classifies dialysis as a high hazard, so the containment device must be an air gap or an RPZ. A double check is a low-hazard device; its approval does not extend to a premises that handles blood-borne and chemical contamination risk (RO reject, disinfectants, dialysis waste). 'It is already there' is not a compliance argument.
But separate the two requirements:
- The 1-inch RPZ on the RO feed is good practice and probably required by the clinic's own infection-control and equipment standards. It protects the building from the RO skid.
- It does not satisfy containment, because containment protects the public main from everything on the premises, and the isolation option in this ordinance is conditioned on the containment device matching the highest hazard.
The trap in this question: answering 'the branch RPZ covers it.' It does not. Conversely, installing the RPZ at the meter does not let the clinic drop the branch RPZ, because high-hazard internal cross connections still need point-of-use protection and because the RO skid may itself create backpressure.
Action: submit a revised plan with the meter device changed to an RPZ (or air gap), keep the branch RPZ, and get written approval of the final arrangement before rough-in.
2. Run the pressure budget. Is the contractor's objection about losing pressure to the top floor valid?
Read the worked answer
Work it, do not assert it.
| Item | Loss (psi) |
|---|---|
| Static main pressure | 62 (available) |
| Elevation, 38 ft x 0.433 psi/ft | -16.5 |
| 2-inch RPZ at 90 gpm | -10 to -12 (use the manufacturer's curve, not a guess) |
| Meter + premise piping, fittings, filters | -5 to -8 |
| Residual at the top floor | roughly 26 to 30 psi |
Judgment: 26-30 psi flowing is generally workable for conventional fixtures. Flushometer valves typically want on the order of 15-20 psi flowing at the fixture, so there is margin. The number that matters is not the top-floor bathroom, though - it is the RO skid's minimum feed pressure and the clinic's required flow, which must be checked against the equipment cut sheet.
If the margin is short: add a booster pump downstream of the RPZ. That is permissible precisely because the RPZ is rated to contain backpressure from the pump. What is not permissible is deleting, bypassing, or downsizing the RPZ to save pressure, or substituting a double check.
Also confirm that the elevation figure is taken to the highest fixture outlet, not the highest floor slab, and that the 90 gpm is realistic peak demand rather than connected load.
3. What administrative obligations attach to this installation once it is approved and built?
Read the worked answer
Before service
- Assembly must be on the supplier's device inventory with make, model, size, serial number, and location.
- Initial test by a certified tester (ASSE 6010 or the jurisdiction's equivalent) before the device is placed in service, with the report filed.
Ongoing
- Annual (or ordinance-specified interval) testing of every testable assembly - the containment RPZ and the branch RPZ are separate line items and both are tested.
- Reports submitted within the ordinance's stated window; a failed or overdue device is a compliance item, not a maintenance suggestion.
- Only testers holding current certification and using a test kit with a current calibration certificate may produce a report.
Responsibility
- The property owner/operator is accountable for compliance even though the contractor installed it and the tester performed the test. The lease should assign this explicitly - in a leased suite, ambiguity here is how devices go untested.
- Records retained per the ordinance; keep them on site and available to the inspector.
Ask the supplier in writing what interval, what report form, and what submission deadline apply, and put the answers in the clinic's maintenance calendar before the doors open.