Insights

Settling unknown service lines from records, before anyone digs

Published October 13, 2026 · Lead Inventory Desk

Small community water systems still list 4,325,243 service lines as lead status unknown, 21.8% of the lines they have reported to EPA. Most of those lines can be settled at a desk, not with a backhoe.

Why the unknown list matters

"Unknown" is an allowed category in the inventory, but it is not a free one. Under the 2024 rule, every system with at least one lead, galvanized requiring replacement or unknown line must write a service line replacement plan by November 1, 2027. Every home on an unknown line gets a notice within 30 days of the baseline inventory and again every year. And every unknown line has to be identified by the system's replacement deadline, which for most systems falls in 2037 (40 CFR 141.84(b)(1)(i), 141.84(c) and 141.85(e)).

So each unknown you settle from records is one less letter a year, one less line in the plan's strategy, and one less possible dig.

Start with the records the rule already names

The rule lists the sources a system must review (40 CFR 141.84(b)(2)):

• construction and plumbing codes, permits and other records that show the service line materials used;
• your own records: distribution maps and drawings, records on each service connection such as tap cards, meter installation records, capital improvement or master plans, and standard operating procedures;
• records of inspections in the distribution system that show service line materials.

Other sources can be used only if your state approves or requires them. EPA's inventory guidance recommends documenting which records you reviewed and when, and noting the record behind each line's category. It also suggests checking how accurate each record type turns out to be: recent records from road construction may be more reliable than decades-old tap cards.

Use the dates that rule lead out

The 1986 Safe Drinking Water Act amendments banned pipe that was not "lead free" in plumbing for drinking water, and states had to enforce the ban within 24 months after June 19, 1986. Some states and towns acted earlier, so EPA recommends checking your state's date (EPA guidance, section 4.2).

The 2024 rule uses the same idea. Lines with records showing installation after June 19, 1988, or after an earlier state or local ban, are left out of the random sample that systems must later inspect to validate their non-lead lines (40 CFR 141.84(b)(5)(i)). A tap date, a permit or a subdivision build record after the ban is often the cheapest evidence you have. Whether a build date alone is enough is your state's call, so ask before you rely on it.

Let routine work fill the gaps

The rule requires systems to record service line and connector materials whenever they see them in normal operations, for example when reading or replacing meters or doing repairs (40 CFR 141.84(b)(2)(v)). EPA lists meter reading, meter repair and replacement, service line and main repairs, and backflow inspections as natural moments to look (EPA guidance, section 3.4). A one-page form, a phone photo and an address are enough. Many small systems can schedule unknown addresses into a regular meter route.

Ask customers, where your state allows it

Property owners can often see the pipe where it enters the building. EPA's "Protect Your Tap" guide walks people through a quick check, and several utilities collect photos from customers to help identify materials (EPA guidance, chapter 5). Use this only where your state accepts it as an identification method.

Field work comes last

For lines that are still unknown, EPA's guidance describes camera inspection through the curb box, and excavation, either a mechanical pothole or vacuum excavation (EPA guidance, sections 5.1 and 5.3). These cost more, take crew time and disturb the line. Any disturbance of a lead, galvanized or unknown line triggers notice and flushing information for the people served (40 CFR 141.85(f)). Coordinating these checks with planned main or meter work saves money.

A practical order

1. Sort every unknown line by what it would take to settle it: records, a look during routine work, customer help, or field work.
2. Work the records first, and write down the record behind every change.
3. Route the next group into normal operations.
4. Budget field work only for what is left, and put the approach in the replacement plan's strategy for unknown lines, which the rule requires (40 CFR 141.84(c)(1)(i)).