What is Selenium in drinking water?

Selenium has 52,594 recorded EPA SDWIS violations across 13,645 public water systems (upper-third volume (> 49,133 violations)).

How many water systems have Selenium violations?

13,645 systems, a wide national footprint (wide footprint (> 8,691 systems)).

Are Selenium violations dangerous?

6.3% are health-based. The rest are monitoring/reporting, still compliance failures, but not the same as an MCL exceedance.

Where does Selenium sit in the national contaminant ledger?

#44 of 157 indexable contaminants by violation volume - upper-third volume (> 49,133 violations), mid load (≤ 5.8 violations per affected system).

Where does this contaminant data come from?

EPA Safe Drinking Water Information System (SDWIS) quarterly extracts. Counts are cumulative compliance records, not a live risk score for a single tap.

Contaminants →

EPA SDWIS High-volume analyte

Selenium in Drinking Water

Compiled by PlainWater · May 15, 2026

13,645 public water systems carry at least one Selenium violation - wide footprint (> 8,691 systems).

Browse all SDWIS contaminants →

EPA contaminant code: 1045

Total Violations

52,594

Systems Affected

13,645

Health-Based %

6.3%

Violations / System

3.9

Selenium standing, high-volume SDWIS third

Selenium sits in the upper third of this extract by raw violation count (52,594), so the national record is thick enough that system-level lists below are a sample of a much larger compliance trail rather than a near-complete inventory. Load sits mid-pack at 3.9 violations per affected system (mid load (≤ 5.8 violations per affected system)). Health-based share is only 6.3% - almost all of this analyte's trail is monitoring/reporting rather than MCL exceedance. Among 157 indexable contaminants, this page is #44 by violation volume. Utilities listed below are ranked by cumulative violation count for this analyte; pair that with population served to gauge household exposure scale.

Nationwide similar contaminants

Nearest by violation volume

Nitrate-Nitrite (52,447) Atrazine (52,999) Barium (50,993) BHC-GAMMA (50,797)

Nearest by systems affected

Cadmium (13,518 systems) Nitrite (13,772 systems) Mercury (13,488 systems) Chromium (13,419 systems)

Selenium: mixed health vs monitoring split

6.3% health-based · 93.7% monitoring/reporting across 52,594 records.

Health-based (6.3%) Monitoring/Reporting (93.7%)

Most Affected Water Systems

System	State	Violations	Population
Valley Estates	TX	204	68
Humphrey, City Of	NE	176	842
Town North Village Water System	TX	167	360
Valley Estates	TX	163	68
Leisure Mountain MHP	NM	127	161
Ridgefield Public Works	WA	114	20,967
Pinedale Estates Dwid	AZ	107	208
Glade, City Of	KS	96	52
Logan, City Of	KS	89	440
Nambe Headstart	NM	83	40
Falfurrias Utility Board	TX	81	4,473
Riverside CSA #122-Mesa Verde	CA	77	766
PA American Audubon	PA	77	8,200
Beverly, City Of	KS	72	135
Mustang Station WS	TX	72	35
Rosa Joint Ventures Water System	NM	68	239
Seven Estates	TX	67	189
Burr Oak, City Of	KS	65	142
Glen Elder, City Of	KS	61	359
Albion, City Of	NE	59	1,700
Asgard Subdivision WA	CO	58	80
City of Davis	CA	57	67,457
Fowler Town Of	CO	57	1,169
Laurel, City Of	NE	56	972
Coal Mountain Water	WV	56	80
Mount Eagle Water Assoc	PA	55	130
Dedham Water Supply	IA	54	221
Franklin Water Systems 3	TX	51	201
Hiawatha Water	WV	51	63
Rising City, Village Of	NE	50	374

Context: understanding water quality data · is my water safe?

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater

Disclaimer: This information is provided for informational purposes only and does not constitute professional advice. Data is sourced from the EPA Safe Drinking Water Information System (SDWIS). Consult a qualified professional before making decisions based on this data.

Read our methodology - how this data is sourced, computed, and verified.

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.