Lithium in drinking water: no federal limit, and 26.6% of systems above EPA's 10 ug/L reference level

If you came here because a headline said a quarter of American water is over a lithium limit, read the next heading first: there is no limit to be over, and the word EPA uses is “screening”.

Is there a legal limit for lithium in tap water?

No. EPA’s UCMR 5 Technical Fact Sheet (EPA 815-F-23-007) states that the agency has not established a non-regulatory drinking water Health Advisory or any regulatory standard for lithium in public drinking water supplies.

Table 2 of the UCMR 5 Data Summary makes the same point in a column: lithium’s Regulatory Level cell is a dash. Five of the PFAS beside it carry MCLs; lithium carries a Health Reference Level of 10 ug/L and nothing else.

A Maximum Contaminant Level (MCL) is the enforceable number in a National Primary Drinking Water Regulation. A Health Reference Level (HRL) is, in EPA’s own glossary, derived during the CCL 5 process for screening purposes and marked non-regulatory. No system is in violation on lithium, because there is nothing to violate.

What does the 10 ug/L reference level actually mean?

It is an arithmetic screening value, and the fact sheet shows the arithmetic. EPA derived a provisional oral reference dose of 2 ug/kg-day through the Provisional Peer-Reviewed Toxicity Value process, applying a composite uncertainty factor of 1,000 to the lowest therapeutic dose associated with adverse effects in patients.

The 10 ug/L follows from that dose, a daily drinking water ingestion rate of 33.8 mL/kg-day, and a default assumption that drinking water accounts for 20 percent of daily lithium intake. EPA’s glossary adds that HRLs are not final determinations about the level necessary to protect any particular population.

There is a second published number worth knowing. EPA’s fact sheet notes that USGS also published a 10 ug/L screening level, and separately a “drinking water only” benchmark of 60 ug/L, which assumes drinking water is the sole source of daily intake.

How many systems were above it, and where?

The commercial laboratory Pace Analytical, writing in April 2026, called roughly 26.6 percent an unusually high rate for any contaminant in any round of UCMR, and read it as a signal that lithium could move toward a Health Advisory and eventually an MCL. That is Pace’s forecast, not an EPA statement. EPA’s own counts, above, are what the percentage rests on.

Geography matters more than the national number. EPA’s fact sheet notes lithium occurs at higher concentrations in certain parts of the country, particularly in groundwater sources in arid locations in the Western United States where geologic formations contain lithium salts.

Which treatment class reduces lithium?

Two EPA documents say different things, three years apart, and the page names both.

The 2023 fact sheet names ion exchange on bench- and pilot-scale literature and does not name reverse osmosis at all. The 2025 review looked at 19 historical pilot- and full-scale studies plus sampling at 13 water treatment plants, 32 sites in total, and found the opposite ranking: reverse osmosis above 90 percent, exchange resins inconsistent. Full-scale evidence is the stronger of the two, so reverse osmosis is the honest answer.

One caveat belongs on the shelf beside it. NSF’s page for NSF/ANSI 58 lists 16 optional reduction claims, from cyst and arsenic through fluoride, perchlorate and radium 226/228, and lithium is not among them. A certified RO unit is certified for total dissolved solids reduction and its listed claims; no maker can hold a lithium claim under that standard, because the claim does not exist. The contaminant-by-contaminant reverse osmosis table covers what the standard does cover.

What should you do first?

1. Find your water system’s UCMR 5 lithium result in EPA’s UCMR 5 Data Finder, filtering by PWS ID or name.
2. Read it against 10 ug/L, remembering EPA rounds to one significant digit, so a result above 15 ug/L rounds to 20 ug/L and counts as above the level.
3. Check your utility’s Consumer Confidence Report: community water systems must report UCMR results there when a contaminant is measured at or above the minimum reporting level, giving the year’s average and range.
4. If you are on a private well, none of the above applies, because UCMR 5 covered public water systems only. Add lithium to a certified laboratory order, as the well water test panel guide sets out.
5. Only then compare units, using published membrane specifications rather than a lithium claim no certification covers.

Lithium is a candidate for regulation, not a regulated contaminant. The number to write down is your own, and the water test report guide covers how to read it next to the rest of the panel.

Frequently asked questions

Sources

1. EPA, The Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) Data Summary: July 2026 (EPA 815-S-26-007) (government or regulatory source)
2. EPA, Technical Fact Sheet: Lithium in Drinking Water, A Resource for Primacy Agencies (EPA 815-F-23-007, October 2023) (government or regulatory source)
3. EPA Science Inventory, Lithium Removal From Drinking Water (AWWA Water Science, 10 February 2025) (government or regulatory source)
4. EPA, Fifth Unregulated Contaminant Monitoring Rule Data Finder (government or regulatory source)
5. NSF, NSF/ANSI 58: Reverse Osmosis Drinking Water Treatment Systems (standards or certification body)
6. Pace Analytical, Making Sense of UCMR 5 Results: Key PFAS Findings, Lithium Concerns and UCMR 6 Signals (22 April 2026) (manufacturer or vendor document)