Magnesium bicarbonate water is made by combining milk of magnesia with cold carbonated water, triggering a simple chemical reaction that dissolves magnesium into a drinkable solution. The process takes about 30 minutes, requires only two ingredients, and yields a concentrate containing roughly 1,500 mg of magnesium per liter that you then dilute before drinking.
Unlike most magnesium supplements you find in pill form, magnesium bicarbonate only exists dissolved in water. It can’t be dried into a powder or pressed into a tablet. That’s why you have to make it yourself.
What You Need
The ingredient list is short: unflavored milk of magnesia and plain carbonated seltzer water. That’s it. But the details matter.
For milk of magnesia, use a plain, unflavored version with no added dyes, sweeteners, or flavorings. The active ingredient is magnesium hydroxide. A standard dose of 3 tablespoons (45 mL) provides enough magnesium hydroxide to react with one liter of carbonated water. Some people prefer to use food-grade magnesium hydroxide powder (96% purity or higher) mixed into water instead of the liquid product, which avoids any inactive ingredients entirely.
For the carbonated water, use unflavored seltzer or club soda in a 1-liter plastic bottle. The bottle needs to be sealable because the reaction requires pressure to keep the carbon dioxide in solution. Glass works but plastic is easier to squeeze and check for firmness. Avoid mineral water or tonic water, both of which contain other dissolved compounds.
The Chemistry Behind It
The reaction is straightforward. Magnesium hydroxide (from the milk of magnesia) reacts with carbonic acid (the dissolved CO2 in seltzer) to produce magnesium bicarbonate and water:
Mg(OH)₂ + 2CO₂ → Mg(HCO₃)₂
Carbonic acid is weak and unstable, which is why you need the water to be well chilled and fully carbonated. Cold liquid holds more dissolved CO2 than warm liquid. If the seltzer has gone flat or is warm, there won’t be enough carbonic acid to fully react with the magnesium hydroxide, and you’ll end up with a cloudy, gritty solution instead of a clear one.
Step-by-Step Instructions
Chill everything first. Put your sealed bottle of seltzer water in the refrigerator for at least a few hours, ideally overnight. Cold carbonated water holds CO2 much more effectively, and that CO2 is what drives the reaction. The milk of magnesia should be at room temperature or cooler.
Shake the milk of magnesia bottle well. The magnesium hydroxide settles to the bottom, so you need it evenly suspended before measuring. Measure out 3 tablespoons (45 mL).
Open the chilled seltzer bottle slowly, pour off just enough liquid to make room for the milk of magnesia (about 2 to 3 ounces), then pour in the milk of magnesia. Cap the bottle immediately and tightly. You want to lose as little carbonation as possible during this step.
Shake the sealed bottle vigorously for 30 seconds, then set it down. Over the next few minutes, the bottle will swell and feel firm as CO2 is released inside. Once it feels pressurized, carefully open the cap to release excess gas, then reseal and shake again. Repeat this process three to four times over about 30 minutes.
The reaction is complete when the liquid turns from milky white to completely clear. If the water is still cloudy, that’s unreacted magnesium hydroxide, meaning not enough CO2 was available. You can add a splash of fresh seltzer, reseal, and shake again to push the remaining magnesium hydroxide into solution. A perfectly clear result means all the magnesium is now dissolved as magnesium bicarbonate.
Diluting the Concentrate
What you’ve just made is a concentrate, not a ready-to-drink beverage. One liter of this concentrate contains approximately 1,500 mg of magnesium and 7,500 mg of bicarbonate. Drinking it straight would almost certainly cause diarrhea, since magnesium hydroxide is the active ingredient in laxatives for a reason.
To make drinking water at a practical concentration, dilute one-third of a liter (about 333 mL or 11 ounces) of concentrate into a 4-liter container of plain water. This yields roughly 125 mg of magnesium and 625 mg of bicarbonate per liter, with a pH around 8.3. For reference, an Australian commercial product called Unique Water uses nearly identical concentrations: 120 mg of magnesium and 650 mg of bicarbonate per liter.
Store both the concentrate and diluted water in the refrigerator, sealed tightly. The magnesium stays dissolved better when cold. If you see cloudiness develop over time, the magnesium is falling out of solution and you’ll need a fresh batch.
Why Bicarbonate Form Matters
The bicarbonate component isn’t just a byproduct of the recipe. Research in kidney physiology has shown that magnesium reabsorption in the body is partly bicarbonate-dependent. In animal studies, when bicarbonate reabsorption dropped by about 41%, magnesium reabsorption fell by roughly 31% alongside it. The correlation between the two was strong (r = 0.82), suggesting that bicarbonate ions actively assist magnesium transport across cell membranes.
This is the core argument for magnesium bicarbonate over other supplement forms. Magnesium oxide, one of the cheapest and most common supplement forms, has notoriously poor absorption. In a study comparing magnesium citrate to magnesium oxide, urinary magnesium (a marker of how much actually entered the bloodstream) was dramatically higher after citrate: 0.22 vs 0.006 mg/mg creatinine over four hours. Magnesium citrate achieved better absorption largely because of its higher solubility. Magnesium bicarbonate, already fully dissolved in water, sidesteps the solubility problem entirely.
Dosage and Side Effects
The recommended dietary allowance for magnesium is 400 to 420 mg per day for adult men and 310 to 320 mg for adult women, combining food and supplements. If you’re drinking the diluted water at 125 mg per liter, two to three liters per day would provide 250 to 375 mg of supplemental magnesium. Most people get some magnesium from food, so this range typically fills the gap without exceeding safe levels.
The main side effect of too much magnesium from any source is loose stools or diarrhea. This is bowel tolerance, your body’s signal that you’ve taken more than it can absorb. If this happens, simply reduce the amount you’re drinking or dilute the concentrate further. Because the magnesium in this water is already dissolved and ionic, it tends to absorb more gradually than a bolus dose from a pill, which can make it gentler on the digestive system.
Tap Water Concerns
If your tap water contains chlorine (most municipal water does), you can use it for dilution but should boil it for about 15 minutes first to drive off the chlorine, then let it cool completely before combining it with the concentrate. Alternatively, use filtered or distilled water for dilution. Chlorine can potentially interfere with the stability of the dissolved magnesium bicarbonate over time.
Troubleshooting Common Problems
A cloudy final product is the most common issue. It means magnesium hydroxide didn’t fully react. The usual culprits: seltzer wasn’t cold enough, had already lost carbonation before you started, or you didn’t shake long enough. Start with the coldest, freshest carbonated water you can find and work quickly when the cap is off.
White sediment settling at the bottom after storage means the water has become supersaturated and magnesium is precipitating out. This happens more readily at warmer temperatures. Keep the bottle refrigerated and sealed. If sediment appears, the water is still safe, but that settled magnesium is no longer in the bioavailable bicarbonate form.
If the bottle feels like it might burst from pressure during shaking, release the gas more frequently. The reaction generates CO2 as a byproduct, and pressure can build quickly in a sealed container. Plastic bottles are safer than glass for this reason.