11.3 Leak Detection & Corrosion Control

Why Leaks and Corrosion Belong Together

Lost water and failing metal are two sides of asset management. Leaks waste treated water, raise energy costs, and can undermine streets. Corrosion thins pipe walls, pits steel tanks, and grows tubercles that shrink diameter and shelter bacteria. TCEQ water operators are expected to understand leak finding, basic audit concepts, and corrosion-control tools used on distribution systems—and to recognize related corrosion issues in wastewater force mains and metallic structures. On exams, a leak question often pairs with a corrosion or flushing question because the same aging cast-iron or steel inventory drives both problems.

Acoustic Leak Detection

Many distribution leaks never surface. Acoustic leak detection uses listening devices on hydrants, valves, and service connections, or correlators that compare leak noise timing between two sensors. Leak sound travels through the pipe wall and the water column; operators interpret pitch, intensity, and correlation results against map distance. Best results come at night when demand noise is low, with known pipe material and accurate distances between fittings. Metal pipe transmits sound farther than plastic; operators must adjust expectations on PVC and HDPE.

Complementary methods include pressure monitoring (sudden drops), district metered area (DMA) night-flow analysis, satellite or aerial sensing in some programs, and visual inspection of wet spots, green strips, and foundation seepage. Acoustic work still needs a skilled operator: plastic pipe dampens sound, soft soils change transmission, and competing noise can mask small leaks. After a suspected hit, crews verify with probing, excavation, or temporary isolation before large street cuts.

Water Audits and Non-Revenue Water

A water audit balances water produced (or purchased) against metered consumption and estimated uses. Non-revenue water (NRW) is water that is produced but not billed. NRW includes:

• Real losses — leaks on mains, services, and tanks; storage overflows
• Apparent losses — meter under-registration, billing errors, unauthorized use
• Unbilled authorized consumption — some flushing, firefighting, or municipal uses, depending on local accounting

Reducing NRW is not only “find every leak.” Meter testing, service-line replacement, pressure management, and faster leak repair all matter. High pressure increases leak volume on existing holes, so pressure reduction in oversized zones can cut real losses without a single excavation. Exam questions often ask you to distinguish real versus apparent losses so you pick the right corrective action—acoustic surveys will not fix a systematically slow residential meter population.

Cathodic Protection and Soil Corrosivity

Corrosion is electrochemical: metal oxidizes where anodes form and electrons flow to cathodes through the metal while ions move through an electrolyte (soil or water). Cathodic protection (CP) forces the entire structure to behave as a cathode.

• Sacrificial (galvanic) anodes — zinc, magnesium, or aluminum alloys corrode preferentially and protect steel or ductile iron when bonded correctly.
• Impressed-current systems — a rectifier drives current through inert anodes to protect large tanks, transmission mains, or coated steel.

Operators verify CP with pipe-to-soil potential readings, rectifier output checks, and anode bed inspection. Coatings and CP work together: a good coating reduces current demand; CP protects coating holidays. A rectifier that shows zero amps is an integrity alarm, not a paperwork issue.

Soil corrosivity rises with moisture, low resistivity, chlorides, sulfates, acidity, and anaerobic bacteria. Utilities use soil resistivity surveys and corrosion coupons when planning metallic mains. Poorly drained clay belts common in parts of Texas can be aggressive toward unprotected iron and steel. Polyethylene encasement on ductile iron is a common external shield against that soil contact.

Linings, Coatings, and Tuberculation

External coatings (polyethylene encasement for ductile iron, tapes, epoxies) isolate pipe from soil. Internal linings (cement mortar, epoxy) protect water quality and hydraulics and slow internal corrosion. Wastewater structures use epoxy or other protective linings against sulfide-driven acid attack on concrete and metal.

Tuberculation is the buildup of corrosion by-products and deposits inside iron mains. Tubercles raise roughness (higher head loss / lower Hazen-Williams C-factor), cut carrying capacity, and create red-water complaints when disturbed. Controlling stable finished-water chemistry (appropriate pH, alkalinity, and corrosion inhibitors such as orthophosphate where used), replacing or lining badly tuberculated pipe, and disciplined flushing all help. Sudden flow reversals in tuberculated grids often release colored water—another reason planned unidirectional flushing beats random hydrant cracking.

Unidirectional Flushing for Water Quality

Routine “open a hydrant” flushing can stir sediment without removing it efficiently. Unidirectional flushing (UDF) closes selected valves so water moves in one planned direction at scouring velocity, sweeping sediment and biofilm toward a discharge hydrant. Crews follow a sequenced map, measure chlorine residual and turbidity, and restore valves carefully so closed valves are not left isolating customers or dead-ending a main unintentionally.

UDF goals include clearer water, restored disinfectant residual, fewer taste-and-odor complaints, and partially recovered hydraulic capacity. Coordination with customers, traffic control, and dechlorination of discharged water (where required) are part of a professional flush program. Tracking flush volumes also feeds the water audit so authorized flushing is not mistaken for unexplained real loss.

Operator Scenario

Night acoustic surveys flag a leak correlation on a 6-inch cast-iron main. The district’s audit shows rising real losses while meters test accurate—so the problem is leakage, not apparent loss. After repair, the crew notes heavy tuberculation in the cut pipe and schedules that grid for unidirectional flushing and evaluation for lining. Separately, a steel ground storage tank’s rectifier alarm shows zero current; without impressed-current CP, external corrosion would accelerate at coating holidays—so electrical repair is an integrity priority equal to the main break. Together, leak repair, CP restoration, and UDF form one asset-management response rather than three unrelated work orders.