Distilled water is essentially free of nitrates. The distillation process removes up to 99.5% of impurities from water, and nitrates are among the compounds left behind in the boiling chamber. If you’re using distilled water to avoid nitrate exposure, whether for infant formula, aquariums, or other sensitive applications, it’s one of the most effective options available.
Why Distillation Removes Nitrates
Nitrates are dissolved salts. They don’t evaporate when water boils. During distillation, water is heated until it turns to steam, and that steam rises into a cooling section where it condenses back into liquid. The nitrates, along with other dissolved minerals and metals, stay behind in the boiling chamber because their boiling points are far higher than water’s. The condensed water that collects on the other side is essentially pure H₂O.
This same principle applies to other inorganic contaminants like lead, iron, calcium, magnesium, and fluoride. Anything that doesn’t vaporize at water’s boiling point gets separated out. It’s a straightforward physical process, and when the equipment is working properly, it’s remarkably thorough.
How Distillation Compares to Other Filtration
Reverse osmosis, ion exchange, and distillation all remove nitrates from drinking water, but they differ in how much they remove. Reverse osmosis systems typically reject 83% to 92% of incoming nitrate. If your source water has extremely high levels (above 110 mg/L of nitrate-nitrogen), reverse osmosis can still leave a measurable amount behind.
Distillation, by contrast, removes virtually everything. Because it relies on a phase change (liquid to gas and back), it doesn’t depend on a membrane’s rejection rate or a resin’s capacity. The result is water with no meaningful nitrate content. For people dealing with well water that tests high for nitrates, distillation provides the most complete removal of the three methods.
Could Nitrates Still End Up in Distilled Water?
In theory, tiny amounts of contamination can occur through a process called carryover, where droplets of boiling water get splashed or carried into the steam before it condenses. Industrial steam systems occasionally deal with this when equipment degrades or pressure drops suddenly. In a home countertop distiller, the risk is minimal as long as the unit is maintained and not overfilled. Commercially bottled distilled water goes through quality controls that make carryover even less likely.
The more realistic concern is contamination after distillation. Distilled water stored in dirty containers, or left open to the environment, can pick up trace contaminants. For practical purposes, though, the nitrate levels in properly produced and stored distilled water are effectively zero.
Nitrate Limits in Drinking Water
The EPA sets the maximum contaminant level for nitrate in public drinking water at 10 mg/L (measured as nitrogen), which equals 45 mg/L of total nitrate. The FDA applies the same limit to bottled water, including bottled distilled water. Nitrate contamination in tap water typically comes from agricultural fertilizer runoff, leaking septic systems, and natural erosion of mineral deposits.
Infants under six months are the most vulnerable to nitrate exposure. High nitrate levels interfere with the blood’s ability to carry oxygen, a condition sometimes called blue-baby syndrome. This is one of the main reasons parents with well water sometimes use distilled water for mixing formula.
Distilled Water for Aquariums
Aquarium hobbyists often turn to distilled water because tap water in agricultural areas can contain nitrates that add to the nitrate load fish are already producing. Using water with zero nitrates as your starting point means you only need to manage the nitrates generated inside the tank by fish waste and decaying food. This can significantly reduce how often you need to do water changes.
If you’re trying to maintain tank nitrate levels around 20 ppm rather than 80 ppm, you’ll need roughly four times as many water changes. Starting with nitrate-free distilled water makes that target more achievable. Keep in mind that distilled water also lacks the minerals fish need, so most aquarists remineralize it before adding it to the tank.
Testing Your Water at Home
If you want to verify that your distilled water is nitrate-free, home nitrate test strips are widely available and inexpensive. Most strips detect nitrate levels starting around 5 to 10 mg/L. Properly distilled water should read at or near zero. Testing is especially useful if you’re distilling your own water at home and want to confirm the unit is working correctly, or if you’ve opened a jug of store-bought distilled water and want peace of mind before using it for a sensitive purpose like infant feeding or a reef aquarium.