Is Longmont, CO Tap Water Safe? Quality & Contaminants

What was found in Longmont's water

The level at the city's main supplier, the highest level anywhere in the city, the EPA limit for each, and where every figure comes from.

Contaminant	Level vs EPA limit	Suppliers	Source
Fluoride	670 µg/L 17% of the EPA limit 4000 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2018	2/4	SYR4
Nitrate	110 µg/L 1.1% of the EPA limit 10000 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2019	2/4	SYR4
Nitrate-Nitrite	88.652 µg/L 0.9% of the EPA limit 10000 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2014 Highest in the city: 100 µg/L — LONGS PEAK WD · 3,200 people · 2014	2/4	SYR4
TTHM	41.45 µg/L 52% of the EPA limit 80 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2019 Highest in the city: 65.73 µg/L — LONGS PEAK WD · 3,200 people · 2019	2/4	SYR4
Total Haloacetic Acids (HAA5)	28.975 µg/L 48% of the EPA limit 60 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2019 Highest in the city: 54.591 µg/L — LONGS PEAK WD · 3,200 people · 2019	2/4	SYR4
Chloroform	35.94 µg/L No EPA limit set Main supplier: LONGMONT CITY OF · 104,178 people · 2018 Highest in the city: 40.9 µg/L — LONGS PEAK WD · 3,200 people · 2018	2/4	SYR4
Barium	10.4 µg/L 0.5% of the EPA limit 2000 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2012 Highest in the city: 18.5 µg/L — LONGS PEAK WD · 3,200 people · 2019	2/4	SYR4
Trichloroacetic Acid	12.525 µg/L No EPA limit set Main supplier: LONGMONT CITY OF · 104,178 people · 2018	2/4	SYR4
Dichloroacetic Acid	9.4035 µg/L No EPA limit set Main supplier: LONGMONT CITY OF · 104,178 people · 2018	2/4	SYR4
Bromodichloromethane	2.714 µg/L No EPA limit set Main supplier: LONGMONT CITY OF · 104,178 people · 2018 Highest in the city: 4.1 µg/L — LONGS PEAK WD · 3,200 people · 2018	2/4	SYR4
Di(2-ethylhexyl) Phthalate	1.456 µg/L 24% of the EPA limit 6 µg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2019	1/4	SYR4
Selenium	1 µg/L 2% of the EPA limit 50 µg/L Highest in the city: LONGS PEAK WD · 3,200 people · 2019	1/4	SYR4
Gross Alpha, Excl. Radon And U	0.6000 pCi/L 4% of the EPA limit 15 pCi/L Main supplier: LONGMONT CITY OF · 104,178 people · 2012	2/4	SYR4
Combined Radium (-226 And -228)	0.2000 pCi/L 4% of the EPA limit 5 pCi/L Main supplier: LONGMONT CITY OF · 104,178 people · 2012	1/4	SYR4
Lead	0.0016 mg/L 11% of the EPA limit 0.0150 mg/L Main supplier: LONGMONT CITY OF · 104,178 people · 2025 Highest in the city: 0.0020 mg/L — LONGS PEAK WD · 3,200 people · 2025	4/4	LCR

Each bar shows the measured level as a share of the EPA limit: green is well under, amber is close to it, red is over. For lead and copper the limit applies to exactly the 90th-percentile figure shown, so red there means a real exceedance. For everything else the limit applies to a running annual average while the figure is the 95th percentile of the system's samples — over 100% is worth reading, but is not by itself a violation. Formal violations are listed separately. These are the utilities' own EPA-reported results, not a city-wide average. A detection means the lab measured the substance — it isn't the same as exceeding a legal limit. Hover a source tag to see the EPA program and years behind each figure.

Water suppliers serving Longmont

Supplier	Population served
LONGMONT CITY OF	104,178
LONGS PEAK WD	3,200
COUNTRYSIDE OF LONGMONT	775
ST VRAIN MHP LLC	544

Frequently asked questions about Longmont tap water

Is Longmont tap water safe to drink?

EPA testing detected 15 contaminants in the water serving Longmont. A detection isn't the same as a violation — most detected levels are within federal limits. Check the level and source for each contaminant above, and your utility's annual Consumer Confidence Report for the official compliance status.

How many water suppliers serve Longmont?

4 public water suppliers report drinking-water monitoring for Longmont, Colorado to the EPA. Each is listed above with its population served.

What contaminants are in Longmont's water?

The contaminants EPA monitoring detected in Longmont include Fluoride, Nitrate, Nitrate-Nitrite, TTHM, Total Haloacetic Acids (HAA5). The full list, with the level at the main supplier and the data source, is in the table above.

Where does this data come from?

Every figure is official EPA drinking-water monitoring — the Lead & Copper Rule, the UCMR-5 nationwide testing program, and the EPA Six-Year Review — not our own testing. Each number is labelled with its source and period.