Open any free plumbing maintenance schedule template and you will find a column headed "recommended frequency" or "suggested interval", filled with tidy numbers: annually, quarterly, every six months. What that column never tells you is where any of those numbers came from — and they do not come from the same place. Some are requirements written into an adopted plumbing code or enforced by a water utility. Some are instructions published by the equipment manufacturer, which is a completely different thing: nobody will cite you for skipping one, but a warranty claim will be denied over it. And some are simply what the trade does, with no code section and no warranty condition behind them at all. Printing all three in one column, in the same typeface, quietly tells a customer that a sump pump test and a backflow assembly test carry the same weight. They do not.
The clearest example is the one most people get backwards. Backflow prevention assembly testing is genuinely a code requirement — IPC 312.10.2 requires reduced-pressure principle, double-check, pressure vacuum breaker and the related assemblies to be tested at the time of installation, immediately after repairs or relocation, and at least annually. But the annual figure in the model code is the floor, not the mandate you actually answer to. Cross-connection control is administered by the water purveyor or the health authority: they decide who is certified to test, what form the report goes on, when it is due, and whether a high-hazard connection needs testing more often than once a year. Test procedures are normally those in the USC Foundation for Cross-Connection Control and Hydraulic Research Manual or AWWA M14. So the honest label on that row is "code requirement — verify the local program", and that is what this builder prints.
Now compare the temperature and pressure relief valve on a water heater, which most templates list one line below it and treat identically. The code requires a listed T&P valve to be installed. The code does not say anybody has to exercise it. The annual test comes from the manufacturer: Watts’ T&P instructions state the valve lever must be operated at least once a year to make sure the waterways are clear, because mineral deposits adhere to the seat and can render the valve inoperative. That is a manufacturer requirement, and the distinction is not academic — it is exactly the document a warranty administrator reads when a tank fails. Same for the anode rod, which is the single maintenance item most tank warranties are conditioned on. This builder labels those rows manufacturer, cites the instruction sheet, and keeps them visually distinct from the code rows.
The hardest cases are the ones where no authority publishes a number at all, and this is where most templates quietly invent one. Grease interceptor service is a regulatory requirement, but the frequency is set locally: the near-universal trigger is the 25% rule — service the unit once accumulated fats, oils and grease plus settled solids reach 25% of its liquid capacity, because past that point the wastewater stops getting the residence time the interceptor was sized for and grease passes straight into the sewer — while the hard calendar deadline comes from the local FOG ordinance, commonly 30 days for under-sink hydromechanical traps and 90 days for in-ground interceptors, whichever comes first. Anode rods are worse: A.O. Smith, Rheem and Bradford White each publish a different inspection interval, and softened or phosphate-treated water shortens all of them, so an averaged figure would match no manufacturer and protect no warranty. This builder ships those rows with the interval field empty and a prompt to fill it in from the local ordinance or the installed equipment’s own manual. A blank you have to complete is worth more than a confident number with nothing behind it, and anything you do type is printed on the export as "you set this" rather than passed off as published.