Why a small water system needs a second tank, and who is required to look inside the first one
Written for Audubon Southwest's White Mountains Water Projects Tour, August 28, 2026. The numbers are as of that day.
Storage is the most misunderstood asset on a small water system. People picture a bucket. It is not a bucket. A tank is doing four separate jobs at once, and a fifth nobody thinks about, and when a system has only one tank it loses all five in the same minute.
This page is written for a board member or a policymaker, and it is about the inspection gap in general. It does not describe the Heber tank, whose failure is under engineering review. If you are studying for the distribution exam, the storage module in the Field Guide covers inspection levels and water age.
Lose the tank, lose all of it
- No peak capacity
- No backup for a well
- No fire flow
- No pressure reference
- Manual operation, 24/7
What redundancy actually means
Not a spare part on a shelf. It is the ability to keep serving people while one thing is broken, and it takes four pieces working together.
- Storage. A second tank, so one failure is an inconvenience.
- Conveyance. A second path for water to travel.
- Pumping. Capacity that does not all fail at once.
- Controls. Something that knows what the others are doing.
Miss the last one and the first three still leave an operator awake for three days flipping switches by hand.
An emergency intertie is not capacity
Design standards are blunt about this. An emergency connection to a neighboring system cannot be counted toward your source capacity, and it only qualifies as emergency capacity if you could already meet demand without it.
Which is the correct rule, and also why a temporary line run overnight to a neighbor's tank is a rescue rather than a plan.
Washington State Department of Health, Water System Design Manual, WAC 246-290-222(3).
Why small systems end up with one of anything
Nothing about a single tank looks like a mistake until the day it is not there.
A second tank is not a second bucket. It is a site, a pad, a pipe run, valves, controls and a permit, which for a district of a few hundred connections is a capital project on the order of a million dollars. So the district builds one, sized for today, and it works. For fifty years it works.
Which is why redundancy is almost never a local decision about risk appetite. It is a funding question, answered by whether outside capital arrives before the asset does.
The million-dollar figure is an operator's estimate for a district of a few hundred connections, not a published engineering figure.
The small-systems page explains why a district that size has nobody on staff to carry that project.
Nobody is required to look inside
AWWA recommends a full inspection every three years. Six states write an interval into rule. Arizona is not one of them.
A comprehensive tank inspection means the tank comes out of service and is drained, or a diver goes in, or a remote vehicle does. Somebody actually looks at the steel: the floor plates, the seams, the roof, the coating, the hatch. When inspection firms report what they actually encounter, the common interval is six to eight years, and a great many tanks have never been inspected at all.
Who requires an internal inspection
| State | Internal inspection |
|---|---|
| Texas | Annually, by system staff or a contractor (30 TAC 290.46(m)(1)) |
| Arkansas | Comprehensive inspection at least every 5 years (ADH WSTG-23, 2023) |
| Alabama | Every 5 years (335-7-7-.04) |
| Missouri | Every 5 years (DNR PUB2112) |
| New Hampshire | Every 5 years (Env-Dw 504.09) |
| Wisconsin | Every 5 years (NR 810.14) |
| Arizona | No interval set in rule |
| Most other states | No frequency set. Left to the utility. |
Rules checked September 2026. Most states set no frequency and leave it to the utility. The sheet handed out on August 28, 2026 listed Arkansas at 2 years, Rhode Island at external annual and internal 5 years, and Ohio at 5 years, from EPA's 2002 compilation of state requirements; those entries are not current rules and are not carried here.
Arizona sets no interval for looking inside a tank. A sanitary survey every three to five years looks at the outside.
What inspectors find when they do look
One firm covering sixty to seventy-five tanks a year in Missouri and southern Illinois reported serious sanitary defects in twenty to twenty-five percent of them.
Most originated at roof hatches and vents that no longer sealed.
Sources: EPA issue paper on finished water storage facilities (2002), including Kirmeyer et al. (1999) and Zelch (2002); Texas 30 TAC 290.46(m)(1), state rules checked September 2026.
Gideon, Missouri, December 1993
Seven nursing-home residents died. An estimated six hundred people, about forty-four percent of the town, fell ill.
Contamination entered a municipal storage tank through openings at the roof hatch and vents. Flushing carried it into the distribution system. It is the case EPA's storage guidance cites, and the failure was a hatch nobody had climbed up to look at.
Clark et al. (1996); Angulo et al. (1997), the CDC field study, which puts the count of people who fell ill above 650.
The arithmetic nobody runs
Set the emotion aside and this is a maintenance economics problem with three numbers in it, and they are not close to each other.
An inspection is a small number. Draining a tank, repairing the floor and recoating it is a larger but still modest number, and it can buy another few decades of service life. Replacing a tank is a number with a comma in it, and it arrives with no notice, usually alongside an emergency, and always in a year the district did not budget for it.
One operator's view
"We have no rule that makes the small number happen. So we keep paying the large one, and we pay it in the worst possible circumstances. A tank inspection requirement with a funded assistance path for systems that cannot afford one. The requirement alone would be another unfunded mandate on a volunteer board. The pair is a policy."
If you sit on a board
Three questions
When was this tank last inspected inside? What did the report say? What is the replacement cost, and is any of it in the reserve? If nobody in the room knows, that is the finding.
If you operate the system
Write it down
Photograph the hatch, the vent screen, the overflow and the coating every year. It costs an hour. It is also how you prove later that a failure was unforeseeable rather than neglected.
If you write the rules
Cheapest lever available
Inspection is the least expensive intervention in the whole asset lifecycle and the only one that reliably converts a catastrophic cost into a scheduled one.
Who wrote this, and why it is on ziptility.com
Blake Anderson founded Mogollon Water Management, a water utility operator in Arizona. Under agreements with each district's elected board, Mogollon runs the day-to-day operation of the Heber DWID and Pinedale Estates DWID systems. Ziptility acquired Mogollon in April 2025; Mogollon runs as its own brand with its own team. Heber DWID uses Ziptility's software. Blake developed and teaches ADEQ's management training track for small-system boards and managers, holds Arizona's Grade 4 treatment and distribution certifications, and sits on WIFA's Federal Program Committee as a small-system representative. Nothing on this page speaks for WIFA or for either district; each district's own notices are on its own website. Every figure here is traceable to the sources below.
Sources
Every number on this page comes from one of these. Estimates are marked where they appear.
- AWWA Manual M42, Steel Water-Storage Tanks (1998): the three-year full inspection recommendation.
- EPA issue paper on finished water storage facilities (2002), including Kirmeyer et al. (1999) inspection-interval findings and Zelch (2002) defect prevalence.
- CDC and EPA accounts of the Gideon, Missouri outbreak, December 1993: Clark et al. (1996); Angulo et al. (1997).
- Washington State Department of Health, Water System Design Manual: storage component definitions, and WAC 246-290-222(3) on emergency interties.
- State rules as cited in the table, checked September 2026: Texas 30 TAC 290.46(m)(1); Arkansas Department of Health WSTG-23 (2023); Alabama 335-7-7-.04; Missouri DNR PUB2112; New Hampshire Env-Dw 504.09; Wisconsin NR 810.14.
- ADEQ sanitary survey guidance (azdeq.gov): the three-to-five-year survey interval.
- The million-dollar figure in "Why small systems end up with one of anything" is an operator's estimate, not a published engineering figure.
Arizona has no comprehensive tank inspection requirement. Corrections: blake@mogollonwater.com.
The sheet as handed out on August 28, 2026 is on the tour page with the other four. Where this page and the sheet differ, the page is current.