AWWA M42 Tank Inspection Intervals, and the Eight States With Stricter Rules
By Marisol Vega, Municipal water operations manager. Reviewed by Amanda McCallister, editor.
Potable Water Tank Inspection & Cleaning | Wastewater & Sewer Diving Last Tuesday, a city council member called to ask why we were 'spending money on a TV inspection' when the tank had been inspected 'just three years ago' by a diver. I had to explain that three years is the AWWA M42 baseline, not a federal law, and that our state has stricter rules. That's the conversation I have far too often. AWWA M42 is a manual of practice. It recommends inspection of finished-water storage tanks at least every three years. That word 'recommends' is doing a lot of work. It's not a regulation. The only people who can set a hard interval are state agencies, and eight states have decided that three years is too long.
What AWWA M42 Actually Says
AWWA M42, 'Steel Water-Storage Tanks,' is the standard reference for design, construction, and maintenance. The inspection interval guidance is buried in there: a routine inspection at three-year intervals, with an emergency inspection after extreme events. Many utilities treat that as a ceiling, not a floor. They think 'three years' is the maximum allowable, but it's actually the minimum recommended. You can go longer if your state allows, but you shouldn't. The manual also points you to AWWA C652 for disinfection after any tank work, and NSF/ANSI 61 for anything that touches potable water. Those are standards you don't skip. A lot of people don't realize that the inspection interval is often driven by the coating warranty. If your coating company gives you a 10-year warranty, they'll want to see an inspection at year three to catch issues early.
The Eight States That Tighten the Rules
Eight states have rules that are stricter than the M42 guidance. Texas is the one everyone knows, and it's the most demanding. Under 30 TAC 290.46(m)(1), each finished-water storage tank must be inspected annually. That's not a suggestion; it's a condition of your operating permit. The other seven states vary — some call for annual inspections, some for every two years, some for specific tests like coating thickness on a set schedule. I keep a chart on my office wall. It's changed twice in the last five years. If you're not checking your state's code, you're flying blind. And no, a federal standard doesn't preempt it.
What a Real Inspection Cycle Looks Like
Here's how I operate. For the 40 tanks I'm responsible for, I run a rolling schedule. Each tank gets a full internal and external inspection at the state-mandated interval — for us, that's annual. But throughout the year, I do a monthly remote check of the exterior and the level sensors. For the internal, I use a combination of a diver for the submerged areas and a rope-access crew for the roof and walls. We're not using divers every time if a tank can be drained and cleaned; we take that route for the larger tanks. The key is to document everything. My inspectors know the difference between a pinhole leak and a rust stain. And we always take coating thickness readings with a magnetic gauge like the PosiTector 6000.
The Texas Rule That Changes Everything
If you operate in Texas, the annual rule isn't just about inspection. It also means you're scheduling repairs differently. You can't wait for a five-year coating failure to show up; you're catching it at 18 months. That's good, but it means we're inspecting in weather that a three-year cycle would avoid. We've done internal inspections in February with ice on the ladder. It's not fun, but the alternative is a permit violation. The state doesn't give you a pass for 'reasonable maintenance.' You either have the inspection on record, or you're in the penalty box. And the inspection has to be done by someone who knows what they're looking at. AWWA M42 gives you a framework, but it's not a substitute for eyes in the tank.
Frequently Asked Questions
Is AWWA M42 a federal requirement? No. It's a manual of practice published by the American Water Works Association. The guidance is 'at least every three years,' but state regulations are the only rules that carry enforcement. How often does Texas require potable water tank inspections? Annual, under 30 TAC 290.46(m)(1). That applies to finished-water storage tanks. You need a dated inspection record on file, or you're out of compliance. What's the difference between AWWA M42 and AWWA C652? M42 is the overall manual for steel water-storage tanks, covering design, construction, and maintenance. C652 is specifically about disinfection of water-storage facilities. You'd use C652 after any tank repair that could introduce contamination. Can I self-certify a tank inspection? That depends on your state. Some allow a professional engineer to sign off; others require a certified operator. Even where self-certification is allowed, the actual internal inspection has to be physically performed. You can't just sign a piece of paper.