The fluoride added to American drinking water is fluorosilicic acid (H₂SiF₆₎, and it is not manufactured on purpose. 

It is a scrubber product: phosphate rock is about 3–4% fluoride, and when sulfuric acid digests that rock to make phosphoric acid for fertilizer, the fluoride leaves as silicon tetrafluoride and hydrogen fluoride gas. Scrub those gases with water and you get fluorosilicic acid. In 2025 the US recovered an estimated 45,000 tons of it from just three phosphoric acid plants. 

In 2026 both ends of that supply tightened at once: overseas production at a leading exporter was interrupted, and US phosphate producers curtailed output at sites that are themselves named fluorosilicic acid producers. 

Because the acid has a shelf life of about one month, nobody can stockpile through it.

This article is about where that chemical actually comes from, why its supply has almost no slack in it, and why two separate things went wrong in 2026 at the same time.

What Utilities Have Actually Done

The useful thing about this shortage is that water systems are regulated, public bodies, so they announce what they are doing and why. The pattern across 2026 is consistent: first dose reduction to conserve, then, where deliveries failed outright, suspension.

Roughly 60% of the United States population receives fluoridated water, so the affected share of the country is not marginal. Dan Hartnett, chief policy officer at the Association of Metropolitan Water Agencies, and Matthew Garbark, director of Baltimore’s Department of Public Works, both described a market sourced from a very small pool of producers. 

That is the part worth explaining, because it is not obvious why a chemical used by most of the country should be so thinly supplied.

Where The Fluoride Actually Comes From

Here is the fact that reframes the whole story: nobody builds a plant to make fluorosilicic acid. It is recovered from the off-gas of fertilizer manufacturing, and the EPA’s own supply-chain profile lays out the chemistry in two steps.

Phosphate rock is mostly fluorapatite, and it carries roughly 3 to 4% fluoride. The primary reaction is the wet process — the same digestion of rock with sulfuric acid that makes phosphoric acid for fertilizer, and that produces an enormous quantity of gypsum as well:

Ca₅(PO₄)₃F + 5 H₂SO₄ –> 3 H₃PO₄ + 5 CaSO₄ + HF

During that reaction the fluoride and the silicon in the rock are mobilised and leave as gases: silicon tetrafluoride and hydrogen fluoride. Those vapours are captured, and when they are scrubbed with water the second reaction happens in the scrubber itself:

SiF₄ + 2 HF –> H₂SiF₆

Two consequences of being a scrubber product. First, the output is set by how much fertilizer someone else decided to make — not by how much fluoride water systems need. Second, it is not even a clean single compound: the EPA notes, citing AWWA, that fluorosilicic acid “is not a discrete compound, but rather an aqueous mixture of fluorosilicated compounds.” The EPA’s own profile describes the material as forming “as a waste stream” when the gases are scrubbed.

So the chain runs: sulfur becomes sulfuric acid, sulfuric acid digests phosphate rock, the rock gives up its fluoride as gas, the gas is scrubbed into fluorosilicic acid, and a tanker truck takes it to a water treatment plant. Every link in that chain is somebody else’s business decision until the last one.

Why The Supply Has No Slack In It

Four structural facts, each independently sourced, explain why a disruption anywhere in that chain shows up quickly at the tap.

That last line is the one that fools people. A buyer looking at a long list of certified suppliers reasonably assumes a deep market. But certification is a quality credential, not a manufacturing capability: the EPA counted 103 NSF/ANSI Standard 60 certified suppliers of fluorosilicic acid against five domestic manufacturing locations. Depth of distribution is not depth of supply.

The EPA Wrote This Down In 2022

This is the part that ought to be better known. In December 2022 the EPA published a supply-chain profile for fluorosilicic acid as part of a series on water-sector chemicals. It assessed the risk of supply disruption and named the mechanism almost exactly as it played out.

“Production of fluorosilicic acid depends on the production of phosphate rock and manufacturing of sulfuric acid. Planned facility downtime at the limited number of domestic manufacturing facilities has resulted in recurring volatility in the supply of fluorosilicic acid.”
— EPA, Fluorosilicic Acid Supply Chain Profile, December 2022

The same document rated the likelihood of disruption as High, noting “previous widespread disruptions in supply that impacted the water sector,” and rated vulnerability as Moderate-High because of “limited domestic manufacturing concentrated in select geographic areas and strong reliance on imports.” The headline risk rating was nonetheless Moderate-Low, because the EPA scored criticality as Low — fluoridation is, in its words, a “discretionary application,” meaning a utility can reduce or stop dosing without the water becoming unsafe to drink.

The forecast was right in substance and wrong in trigger. The EPA expected planned facility downtime to be the thing that wobbled supply. What arrived in 2026 was unplanned: an interruption at a major overseas producer, and a wave of curtailments at domestic phosphate plants driven by the price of sulfur. The vulnerability the document identified — too few plants, heavy import reliance, no ability to stockpile — was the correct diagnosis regardless of which shock found it.

Both Ends Tightened At Once

Two independent things happened in 2026, and the reason this shortage is described by water managers as unprecedented is that they happened together.

The import leg. Fluorosilicic acid is mainly produced overseas and imported by US distributors, and in the spring of 2026 production at one of the world’s leading exporters was interrupted when a substantial part of the workforce at a major facility became unavailable. Reporting by NPR and member stations in April traced the US shortage directly to that interruption. It is worth being careful with trade figures here: the EPA notes that import and export data specific to fluorosilicic acid is not available, because it is reported inside a broader customs category for inorganic acids other than hydrogen fluoride. Within that broader category in 2021, the largest exporters were China at 92 million kg and Israel at 40 million kg, with the United States the fourth-largest importer.

The domestic leg. At the same time, the American phosphate industry was curtailing production — and for reasons that have nothing to do with fluoride. Sulfur, which is the dominant cash cost in making sulfuric acid, became expensive enough that converting it into fertilizer stopped making money. By August, Mosaic had curtailed or idled four phosphate facilities: Bartow and Riverview in Florida, and Faustina and Uncle Sam in Louisiana. We covered that decision, and the reason an idled acid plant is unexpectedly hard to restart, in our piece on why those acid plants were switched off rather than broken.

The connection that has gone largely unremarked. Those are not unrelated industries. The EPA’s profile records that domestic fluorosilicic acid manufacture has historically taken place in Florida, Louisiana, North Carolina and Wyoming, by J.R. Simplot, Mosaic and PCS Phosphate — and it identifies the Mosaic phosphoric acid plants in Florida and Louisiana among the sites from which the acid is derived. Three of the four facilities on the August curtailment list — Bartow, Riverview and Uncle Sam — sit in that same small population of phosphoric acid plants. So the domestic fallback for a disrupted import stream was contracting at precisely the moment it was needed. WSSC Water said as much in its April notice, attributing the disruption to both reduced domestic production and lower output from other producers.

One further piece of context makes the fragility plainer. The United States has been 100% net import reliant for fluorspar — the conventional mineral source of fluorine chemistry — for years running, excluding sales from stockpiles. Recovered fluorosilicic acid is genuinely useful here: USGS counts the 45,000 tons recovered in 2025 as equivalent to roughly 73,000 tons of 100% calcium fluoride, and one operation in Aurora, North Carolina makes hydrogen fluoride from it. Domestic fluorine chemistry leans on this scrubber stream more than its reputation as a waste product suggests.

What We Are Watching Next

1. Whether the curtailed phosphate capacity comes back. Domestic fluorosilicic acid recovery is a passenger on phosphoric acid run rates. Restarts at the Florida and Louisiana plants are the leading indicator for the domestic leg.
2. The sulfur price. It is the input that decides whether those plants are worth running at all, and therefore whether the scrubbers are running.
3. Utility notices rather than trade data. Because the customs category is broader than the product, public dose-reduction notices from water systems are a faster and more honest signal than import statistics.
4. Lead times on industrial fluoride chemistry. Aluminium fluoride, fluorosilicates and hydrogen fluoride all draw on the same stream; pressure tends to appear there before it appears in price.

Read the full article here, written by Andre Taki at Alliance Chemical: https://alliancechemical.com/blogs/news/fluorosilicic-acid-shortage-2026-fluoride-phosphate-coproduct