Electrolyzed reduced water (ERW) is water produced at the negative electrode (cathode) during electrical water splitting. It contains dissolved hydrogen gas, has an alkaline pH, and carries a negative electrical charge. The name breaks down simply: “electrolyzed” because it went through electrolysis, and “reduced” because a chemical reduction reaction at the cathode is what creates it. ERW is sometimes marketed as alkaline ionized water or hydrogen-rich water, though those terms aren’t perfectly interchangeable.
How ERW Is Made
The process starts with basic water electrolysis, which uses electricity to split water molecules into hydrogen gas and oxygen gas. An electrolysis unit contains two electrodes submerged in water, separated by a special membrane that ions can’t cross. When current flows, hydrogen gas forms at the cathode and oxygen gas forms at the anode. The membrane keeps the two sides from mixing, so you end up with two distinct types of water.
The cathode side produces ERW: alkaline, hydrogen-rich, and low in dissolved oxygen. The anode side produces acidic, oxygen-rich water that’s sometimes used for cleaning or disinfection but isn’t meant for drinking. Home electrolysis units (often called “water ionizers”) perform this same process on tap water, typically using platinum-coated titanium electrodes.
Key Physical Properties
Three measurable characteristics define ERW and distinguish it from regular tap water:
- pH: ERW ranges from slightly alkaline up to about 11.5, depending on electrolysis intensity and the mineral content of the source water. For drinking, guidelines in countries like Japan recommend staying at or below pH 9.8 to avoid potential issues like elevated potassium levels in the blood.
- Dissolved hydrogen: Typical units produce water with 0.4 to 0.9 parts per million (ppm) of dissolved hydrogen gas. Higher-powered units can push levels closer to 1.6 ppm. Regular tap water contains essentially zero dissolved hydrogen.
- Oxidation-reduction potential (ORP): ERW carries a strongly negative ORP, ranging from about −300 millivolts to over −800 millivolts. A negative ORP means the water has electron-donating capacity, which is the basis for claims about its antioxidant properties.
What Makes It Different From Other Hydrogen Water
You can also dissolve hydrogen gas into water by bubbling it in directly, using magnesium tablets, or pressurizing it into sealed pouches. These products are often labeled “hydrogen-rich water” or “hydrogen water.” ERW overlaps with them because dissolved hydrogen is a major component of both, but they aren’t identical.
Cell studies have found that ERW shows stronger ability to neutralize harmful reactive oxygen species than hydrogen water at the same dissolved hydrogen concentration. When researchers removed the dissolved hydrogen from ERW, it still retained some of its cell-protective activity. However, when the water was heated to high temperatures (autoclaved), that residual activity disappeared. This suggests ERW contains something beyond just hydrogen gas that contributes to its effects, likely trace platinum nanoparticles shed from the electrodes during electrolysis. The concentrations are extremely small (around 0.2 parts per billion), but researchers have proposed they may interact with cells in ways that activate the body’s own antioxidant defenses.
Proposed Health Effects
Most of ERW’s proposed benefits center on its antioxidant activity. Reactive oxygen species are unstable molecules your body naturally produces during metabolism. In excess, they damage cells and contribute to inflammation and aging. The dissolved hydrogen in ERW appears to selectively neutralize some of these molecules, at least in laboratory settings.
A 2024 review in the journal Antioxidants summarized the human research to date. In patients with type 2 diabetes, drinking ERW was associated with improved insulin resistance and lower levels of lactate, a marker of metabolic stress. In patients with end-stage kidney disease undergoing dialysis, it appeared to boost antioxidant defenses, reduce inflammatory markers, and improve quality of life by lowering fatigue and the risk of certain complications.
These findings are promising but limited. Most human studies have been small, and researchers generally attribute the therapeutic effects to the dissolved hydrogen rather than the alkaline pH. A comprehensive 2022 review in the International Journal of Molecular Sciences concluded that molecular hydrogen is the “exclusive agent responsible for the therapeutic effects” of ERW, meaning the alkalinity itself likely isn’t doing the heavy lifting.
Safety Considerations
ERW produced within a moderate pH range (roughly 8.5 to 9.5) is generally considered safe for regular consumption. The concern arises at higher pH levels. Governmental guidelines, particularly in Japan where water ionizers have been used for decades, advise against drinking ERW above pH 9.8. At very high alkalinity, there’s a risk of hyperkalemia, a condition where potassium levels in the blood become dangerously elevated. This is especially relevant for people with kidney problems, who may not be able to clear excess minerals efficiently.
Most home ionizer units allow you to select the pH level, so staying within a safe range is straightforward if you pay attention to the settings. If your unit doesn’t display the pH, portable test strips or drops can give you a rough measurement.
Practical Limitations
The biggest practical challenge with ERW is that dissolved hydrogen doesn’t stick around. Hydrogen is the smallest molecule in existence, and it escapes from water readily, especially when the water is exposed to air or agitated. This means ERW is best consumed soon after production. Storing it in an open glass on your counter for hours will leave you with alkaline water that has lost most of its hydrogen content.
If you’re using a countertop ionizer, drinking the water within minutes of production gives you the highest hydrogen concentration. Sealed containers slow the loss but don’t stop it entirely. This is one reason some people opt for hydrogen tablets or sealed hydrogen water pouches instead, though as noted above, these products may lack the additional trace components that give ERW its edge in lab studies.
The mineral content of your source water also matters. Electrolysis works by moving dissolved minerals toward the electrodes, so very soft or distilled water won’t produce meaningful results. Hard water with plenty of dissolved calcium and magnesium tends to produce ERW with higher pH and more dissolved hydrogen.