Water system modeling and water loss analysis for Texas utilities

What it covers

Two questions about an existing system. Can it hold pressure and fire flow as demand grows? And where does the water go that it produces but never bills?

A hydraulic model answers the first. Ours are built in EPANET, the EPA's public domain software, unless a client or agency asks for WaterGEMS. The model shows the flow in every pipe, the pressure at every node and the level in every tank over time. We run average day, maximum day, peak hour, and maximum day plus fire flow, today and at buildout.

A water loss analysis answers the second. Real losses are physical: main breaks, leaks, service line breaks and tank overflows. Apparent losses are water used but not counted: meter error, billing errors and unauthorized use. Each has a different fix. A new meter program will not stop a leaking main, and a leak crew will not fix a billing system that misreads meters.

The gap is common. When MES interviewed 14 water providers in Colorado and Texas, half were dealing with water losses they had not identified.

For new mains, extensions and fire flow for a development, see water distribution. For a new system's wells, storage and TCEQ approval, see public water system design. Outside Texas, see our water loss work in Colorado.

How Texas tracks water loss

Texas Water Code §16.0121 requires a retail public utility that provides potable water to file a water audit with the Texas Water Development Board (TWDB). TWDB's rules, 31 TAC §§358.10 to 358.15, set how:

• Every year by May 1 if the utility has more than 3,300 connections, or has an outstanding TWDB loan, loan forgiveness agreement or grant.
• Every five years by May 1 if it has 3,300 or fewer connections and no TWDB assistance.
• Who prepares it. A person who has completed TWDB's free water loss audit training.
• Validation. A utility filing every year because of TWDB assistance, or applying for assistance, needs its latest audit validated within 180 days of submittal or before TWDB considers its funding request, whichever comes first. TWDB staff validate it, or a separate person trained and certified to validate.
• Thresholds. Real loss must stay under 30 gallons per connection per day where a system has 32 or more connections per mile, and under 57 gallons where it has fewer. Apparent loss is measured against an allowed figure calculated for each utility.

The audit is also a funding gate. A utility that fails to file, or to correct an incomplete audit, cannot get TWDB financial assistance for water supply projects until a complete audit is accepted. If real or apparent loss meets or exceeds the threshold, part of any TWDB assistance for a water supply project must go to reducing the loss, unless the board grants a waiver. The rules count a detailed water loss assessment, pipe or meter replacement, and better monitoring as ways to reduce it. TWDB also offers technical help with audits and lends leak detection equipment.

When you need one

• The system loses more water than it bills, and nobody can say how much or where.
• Your TWDB audit shows loss at or over the threshold, and a funding application is coming.
• Pressure drops at the far end or on high ground as new customers connect.
• A hydrant fails a fire flow test, or the fire code official asks for a flow the system may not deliver.
• The board wants a repair list it can budget and fund, not a list of every old pipe.

What we do

1. Start with the records. We balance source meter readings against billed and unbilled use, using the AWWA M36 water audit method, and grade how reliable each number is. Weak data is the first finding, because it decides what to check in the field.
2. Split real loss from apparent loss. We review meter records, billing data, and metered and unmetered addresses, and check where meters were last tested. The split decides whether the money goes to pipe or to meters.
3. Build and calibrate the model. Demands come from meter or billing records. Tanks, pump curves and pressure reducing valve settings come from the field. We compare the model with hydrant flow tests wherever they exist. A model with no field data is issued as unvalidated, and the report says so.
4. Find where the problems sit. Leakage and main breaks rise with pressure, so the model shows where pressure zones or pressure reducing valves would cut both. It also shows which segment controls a fire flow shortfall, so the fix is that segment, not the whole street.
5. Rank the fixes. We rank replacement by break history, condition and model results, and prepare a budget estimate for the critical repairs. The ranked list is built to drop into a capital plan or a funding application.
6. Check and seal. An engineer who did not write the report checks it before it is issued. It is sealed when it goes to a regulator or is relied on for design.

What you get

• A water loss analysis that splits real from apparent loss and shows where each one concentrates.
• A hydraulic model, calibrated to field data or clearly marked unvalidated, and a report that names the criteria it was checked against.
• A ranked list of repairs with a budget estimate, ready for the owner's budget and the next funding application.

What affects time and cost

• The data you already have. Twelve months of source meter readings for the same period as billing, meter test dates, billed and unbilled use kept apart, a current map of mains and valves, and a log of breaks and repairs. Each gap is work before the analysis can start.
• Metering. An unmetered system, or one with untested source meters, needs metering before losses can be tracked.
• Field data for the model. Hydrant flow tests, with tank levels and running pumps recorded, turn a draft model into a calibrated one.
• The system's shape. Each pressure zone, booster and pressure reducing valve needs settings that match the field.
• The funding calendar. A TWDB application needs a filed audit, and validation if the rules call for it. TWDB decides audits, waivers and funding, so we never promise an outcome or a date.