City of Louisville☆

Where the water comes from

Facility	Kind	Water
MARSHALL LAKE	Intake	Surface water
LOUISVILLE RESERVOIR	Intake	Surface water

These are EPA's facility records, not DWR structures. Which decreed rights sit behind an intake is the next phase; nothing here is inferred.

DWR structures that name this system

Source Probable join · fetched 2026-10-06 · matched on DWR's recorded contact or an EPA intake name; verify on the dossier

10 structures on DWR's record name this system as their contact (9) and 1 matches an EPA intake by name. A match says who DWR lists, not who owns the water: a ditch company can own the headgate while the system owns shares, and a consultant can be the contact. The dossier holds the decree.

Compliance record

Source Register of another agency · fetched 2026-10-07 · verify at EPA ECHO ↗

EPA's own summary: violations in 1 of the last 12 quarters.

What happened

All 2 violation records on file, grouped into the 2 distinct things EPA's codes describe. Dates are the compliance period the violation is filed against.

Every violation record, as filed (2 of 2)

Compliance period	What	About	Kind	Status	Measured
2021-12-01 – 2021-12-31	Treatment Technique (SWTR and GWR)	SWTR	health-based	returned to compliance (2022-02-07)
2021-12-01 – 2021-12-31	Single Turbidity Exceed (Enhanced SWTR)	Ieswtr	health-based	returned to compliance (2022-02-07)

What the regulator did about it

28 enforcement actions on this system's federal record. In Colorado the state is the primacy agency, so most actions are the state's; EPA acts directly on tribal systems and when it steps in.

20 most recent of 28; the rest are on the ECHO report.

Lead and copper

The latest 90th-percentile lead result is 0.0 mg/L (sampling period ending 2025-12-31) against an action level of 0.015 mg/L, below it. 13 results on file.

The action level is not a health limit: it is the level at which the rule requires a system to act (corrosion control, public education, and in some cases replacing lead service lines). Lead mostly enters water from household plumbing, so a system-wide percentile does not tell you what comes out of one tap.

Violation, enforcement and lead/copper records are EPA SDWIS federal reporting, fetched monthly; the summary is EPA ECHO. Code names come from EPA's own REF_CODE_VALUE table. SDWIS carries violations, not routine sample results — nitrate, disinfection by-product and PFAS values are not in it, and a clean record here means nothing was reported as a violation, not that nothing was ever detected. For what was measured, ask the system for its Consumer Confidence Report.

PFAS and lithium: EPA's UCMR 5 monitoring, 2023–2025

Source Register of another agency · fetched 2026-10-09 · verify at EPA UCMR occurrence data ↗

8 samples, 240 results, 2023-03-08 to 2024-05-29. No PFAS was detected at the reporting limits; lithium was not detected.

Rows shown: every detected contaminant plus the regulated PFAS and lithium; the rest were below their reporting limits. These are UCMR monitoring samples, not compliance samples. EPA's April 2024 rule set 4.0 ng/L (0.004 µg/L) for PFOA and PFOS, the same as UCMR 5's reporting limit, so any detection of either is at or above it; the rule's compliance date and its other limits have been under revision since 2025 and are not applied here. State PFAS sampling is on CDPHE's pages ↗.

Common questions

Who provides drinking water in Louisville, Colorado?

The City of Louisville is the public water system serving 20,975 people in Boulder County, from surface water. Its EPA public water system id is CO0107487.

Where does the City of Louisville get its water?

The City of Louisville reports surface water as its primary source. EPA lists its source facilities as MARSHALL LAKE, LOUISVILLE RESERVOIR.

Does the City of Louisville have any drinking water violations?

EPA's compliance record shows no open health-based violations for the City of Louisville at the last monthly fetch. Older and non-health-based entries, if any, are listed on this page.