4.6 Storage Tank Inspection, Meters, Services & Distribution Appurtenances
Key Takeaways
- Finished water storage tanks should be inspected at least every three to five years, with the interior inspected by drained entry, diver, or remotely operated vehicle under a confined space and potable water protocol.
- Air and vacuum release valves protect a main from column separation and from collapse during draining, and a plugged combination air valve is a common cause of unexplained pressure surges.
- Altitude valves close automatically when a tank reaches full level, while pressure reducing valves hold a set downstream pressure independent of upstream pressure.
- The Lead and Copper Rule Revisions required all community and non-transient non-community systems to complete a service line material inventory by October 16, 2024, classifying each line as lead, galvanized requiring replacement, non-lead, or unknown.
- Displacement meters are accurate at low flow and are the standard residential meter, while turbine meters handle high flow but under-register at low flow, which is why compound meters combine both.
Storage Tank Inspection, Meters, Services & Distribution Appurtenances
The ABC Water Treatment outline lists "water storage tanks," "valves (e.g., backflow, control valve, isolating, throttling, pressure regulation)," and "maintain facility and process control water meters" among the equipment tasks an operator must inspect, maintain, and operate. This section covers the asset-management side of those items - what breaks, how it is inspected, and what the records must show.
1. Finished Water Storage Tanks
Inspection program
| Inspection | Frequency | Scope |
|---|---|---|
| Routine site check | Monthly to quarterly | Fencing, hatches locked, vents and overflow screened, no ponding, cathodic protection reading, no visible leakage |
| Exterior inspection | Annually | Coating condition, corrosion, structural connections, ladder and safety climb, roof and hatch seals, sample tap |
| Comprehensive interior inspection | Every 3 to 5 years | Sediment depth, coating condition and holidays, corrosion, structural welds and rivets, inlet/outlet condition, mixing pattern |
| Cleaning and disinfection | As indicated by inspection, commonly 3 to 5 years | Remove sediment, repair coating, disinfect per AWWA C652 |
Interior inspection methods, in order of cost and disruption:
- Remotely operated vehicle (ROV) - a submersible camera. The tank stays in service, but coating adhesion cannot be assessed by camera.
- Potable water diver - a diver in a fully encapsulating dry suit disinfected per protocol. The tank stays in service. Divers can measure sediment and probe coatings.
- Drained entry - the only method that supports full coating assessment, dry-film thickness measurement, and welding repair. It is a permit-required confined space entry and takes the tank out of service.
Sanitary defects to look for
- Vents must be screened (24 mesh) and turned down; a failed vent screen is a direct pathway for insects, birds, and rodents.
- Overflow pipes must be screened and must discharge over an air gap, never be piped directly into a storm sewer or drain - that is a cross-connection.
- Hatches must be locked, curbed, and gasketed, with the cover overlapping the curb downward.
- Roof drainage must not pond over hatches or seams.
- Sediment accumulation provides chlorine demand, harbors bacteria, and is the reason many tanks fail total coliform samples.
Coatings and cathodic protection
Interior coatings on potable tanks must be NSF/ANSI 61 certified. Modern systems are typically epoxy or polyurethane; older tanks may have lead-bearing or coal tar coatings, and removal is then a regulated lead or hazardous-material job with containment. Steel tanks in submerged service use impressed-current or sacrificial anode cathodic protection; a routine operator task is reading and logging rectifier voltage and current.
Turnover and water quality
Storage exists for fire flow, equalization, and emergency supply - but volume that never moves becomes aged water. Practical controls include lowering the operating band to force turnover, installing active mixing systems, changing from a common inlet-outlet to separate inlet and outlet piping, and, for chloraminated systems, monitoring for nitrification with nitrite, total chlorine, and heterotrophic plate count.
2. Valves and Appurtenances
| Device | Function | Operator issues |
|---|---|---|
| Gate valve | Isolation, fully open or fully closed | Exercise annually. A valve that has not been operated in a decade will not close when a main breaks. Record turns to close and compare to expected |
| Butterfly valve | Isolation and throttling | Slow closure required; fast closure causes water hammer |
| Check valve | Prevents reverse flow | Slamming on pump shutdown is a major surge source; use spring-assisted or slow-closing types |
| Pressure reducing valve (PRV) | Holds a constant downstream pressure regardless of upstream pressure | Pilot systems foul; a chattering PRV indicates it is sized too large for the flow |
| Pressure sustaining valve | Holds a minimum upstream pressure | Protects an upper zone from being drained by a lower zone |
| Altitude valve | Closes automatically when a tank reaches its set full level | Prevents overflow; a failed altitude valve is a common cause of tank overflow events |
| Air release valve | Continuously vents accumulated air at high points under pressure | Small orifice; plugs easily |
| Air/vacuum valve | Large orifice; exhausts air during filling and admits air during draining | Without it, draining a main can collapse it |
| Combination air valve | Both functions in one body | The standard at high points |
| Blow-off / flushing hydrant | Dead-end flushing | Must have an air gap; a submerged blow-off is a cross-connection |
Why air valves matter more than they look. Trapped air at a high point reduces the effective pipe cross-section, increasing headloss; and a moving air pocket can cause a violent surge when it is suddenly expelled or compressed. A vacuum valve that fails to open during a rapid drawdown lets atmospheric pressure crush a large-diameter main, and it also allows backsiphonage of anything connected to the depressurized line.
Valve exercising programs should record valve number, location, direction, number of turns to close, condition, and whether it seated. Utilities target a full cycle of the system every one to three years, prioritizing critical isolation valves.
3. Service Lines and the Lead Inventory
| Material | Era / notes |
|---|---|
| Lead | Pre-1950s in many areas; banned for potable use by the 1986 SDWA amendments |
| Galvanized iron/steel | Corrodes internally; "galvanized requiring replacement" if it is or was downstream of a lead service line, because it adsorbs and later releases lead |
| Copper with lead solder | Lead solder banned in 1986; joints remain a lead source in older homes |
| Copper, Type K | Standard for new services |
| Plastic - PE, PEX, CPVC | Modern; must be NSF/ANSI 61 certified |
The service line inventory. The Lead and Copper Rule Revisions required every community and non-transient non-community water system to prepare a service line material inventory by October 16, 2024, classifying each service line - both the utility-owned and the customer-owned portion - as lead, galvanized requiring replacement, non-lead, or lead status unknown. The inventory must be made publicly accessible, updated, and used to drive replacement planning and customer notification. Unknowns must be investigated over time, and the LCRI accelerates replacement obligations beginning with the November 2027 compliance date.
Partial lead service line replacement - replacing only the utility side - is discouraged and in many cases prohibited, because disturbing the line and creating a galvanic couple between new copper and remaining lead can increase lead release for months.
4. Meters
Types
| Meter | Principle | Best range | Notes |
|---|---|---|---|
| Positive displacement (nutating disc, oscillating piston) | Fixed volume per cycle | Low flow | Standard residential meter; accurate at trickle flows; wears with sand |
| Single-jet / multi-jet | Vanes driven by jets | Low to moderate | Common in small commercial |
| Turbine | Rotor speed proportional to velocity | High flow | Under-registers at low flow; used for irrigation and industrial |
| Compound | Displacement chamber plus turbine with a changeover valve | Full range | For customers with both low overnight and high daytime flow |
| Electromagnetic | Faraday's law; requires conductive fluid | Full range, bidirectional | No moving parts, no headloss; the standard for plant and master metering |
| Ultrasonic (transit-time) | Time difference of sound with and against flow | Full range | No moving parts; clamp-on versions permit non-invasive checks |
| Venturi / orifice / propeller | Differential pressure or mechanical | Moderate | Older plant metering |
Accuracy and testing
AWWA standards set new-meter accuracy at approximately 98.5 to 101.5 percent in the normal flow range and 95 to 101 percent at the minimum test flow. Meters lose accuracy in one direction - they slow down and under-register - so an untested meter population is quietly giving water away.
Typical testing and replacement intervals: small residential meters every 10 years or by volume registered; large meters (3 inch and above) annually; and plant master meters annually, with calibration traceable and documented.
5. Water Loss and Non-Revenue Water
The AWWA water audit method replaces the old "unaccounted-for water" percentage with a structured balance:
- System input volume (corrected for master meter error)
- minus authorized consumption (billed metered, billed unmetered, unbilled metered, unbilled unmetered - for example, firefighting and main flushing)
- equals water losses, split into:
- Apparent losses - customer meter under-registration, data handling errors, and unauthorized consumption. These are revenue losses, valued at the retail rate.
- Real losses - leakage on mains, services, and storage overflows. These are production cost losses, valued at the marginal cost of treatment.
Non-revenue water = billed authorized consumption subtracted from system input volume.
Why the distinction matters operationally. Apparent losses are fixed with a meter testing and replacement program and with billing system audits. Real losses are fixed with leak detection surveys - acoustic correlators, leak noise loggers, district metered areas with minimum-night-flow analysis - and with pressure management, since leakage rate rises with pressure. Chasing the wrong category wastes the budget.
A distribution main is being drained for repair and the crew reports the pipe made loud noises and a section was found deformed after the work. Which appurtenance most likely failed?
A commercial customer has very low overnight flow and very high daytime flow. Which meter type is designed for this pattern and why?
Under the Lead and Copper Rule Revisions, what were community water systems required to complete by October 16, 2024?