Magnesium water is made by dissolving magnesium hydroxide (milk of magnesia) into carbonated water, where the carbon dioxide reacts with the magnesium to create a dissolved, drinkable form of magnesium. The process takes about 30 minutes of hands-off time and requires just two ingredients. The result is a clear, slightly mineral-tasting water you can sip throughout the day as a calorie-free magnesium source.
What You Need
The recipe calls for two things: plain carbonated water (seltzer) and magnesium hydroxide. For the carbonated water, use unflavored seltzer or sparkling water with no added sugars or sweeteners. Club soda works but often contains added sodium, so check the label if that matters to you.
For the magnesium hydroxide, you have two options. The easiest is a bottle of plain milk of magnesia from any pharmacy. Use the unflavored version with no added colors, sweeteners, or inactive ingredients beyond purified water. The other option is food-grade magnesium hydroxide powder, which some people prefer because it contains nothing else. Either works the same way chemically.
Step-by-Step Instructions
Start with a 1-liter (or 1-quart) bottle of cold seltzer. Colder water holds more carbonation, and you need that carbon dioxide for the reaction. Open the bottle slowly to minimize fizz loss.
If using milk of magnesia liquid, shake the bottle well, then measure out 3 tablespoons for every 2 liters of seltzer (roughly 1.5 tablespoons per liter). If using magnesium hydroxide powder, use half a teaspoon per liter. Pour the measured amount into the seltzer.
Cap the bottle tightly and shake it vigorously for 15 to 30 seconds. The water will turn cloudy white. Set the bottle down and leave it alone for about 15 to 30 minutes. During this time, the dissolved carbon dioxide reacts with the magnesium hydroxide to form magnesium bicarbonate, which is soluble in water. When the reaction is complete, the water turns completely clear again. If it’s still cloudy, shake it once more and wait another 15 minutes. A fully clear bottle means the magnesium has dissolved.
Why the Carbonation Matters
Magnesium hydroxide on its own doesn’t dissolve well in plain water. That’s why milk of magnesia looks chalky and white. The carbon dioxide in seltzer provides the key ingredient: it reacts with the magnesium hydroxide to produce magnesium bicarbonate, a form that dissolves completely. Once the reaction finishes, the carbonation is mostly used up, so the final product is still or only lightly fizzy. You’re essentially trading the carbonation for dissolved magnesium.
This is the same form of magnesium found naturally in some mineral springs. Certain European mineral waters contain over 150 mg of magnesium per liter, sourced from underground rock in exactly this way. The DIY version replicates that chemistry in your kitchen.
How Much Magnesium You’re Getting
A liter of homemade magnesium water made with the ratios above contains roughly 100 to 130 mg of elemental magnesium, depending on how much magnesium hydroxide you use and how completely the reaction finishes. That’s a meaningful amount. Most adults need between 310 and 420 mg of magnesium per day, so drinking a liter and a half covers a significant portion of your daily needs.
A clinical trial in postmenopausal women tested a similar concept: participants drank 1,500 to 1,800 mL daily of water supplemented with 120 mg/L of magnesium (as magnesium bicarbonate). That delivered 180 to 216 mg of magnesium per day, and the volume was well tolerated by all subjects over three months. This gives a useful reference point for what a reasonable daily intake of magnesium water looks like.
Storage and Shelf Life
Keep your finished magnesium water in a sealed bottle in the refrigerator. Because the magnesium is held in solution partly by the remaining dissolved CO2, leaving the cap off or storing it at room temperature can cause the magnesium to slowly precipitate back out, turning the water cloudy again. A tightly sealed, refrigerated bottle stays clear and stable for at least a week, though most people make a fresh batch every few days.
If your stored water turns slightly cloudy, it hasn’t gone bad. It just means some magnesium has come out of solution. You can shake it up and drink it, but the magnesium won’t be as well dissolved. For the best results, make smaller batches you’ll finish within a few days.
Digestive Side Effects
Magnesium hydroxide is the active ingredient in milk of magnesia, which is sold as a laxative. At the concentrations used in magnesium water, the laxative effect is much milder, but it’s not zero. In the clinical trial mentioned above, about 24% of participants drinking the magnesium-supplemented water experienced diarrhea over the study period, compared to 15% in the control group drinking plain spring water. The difference is real but modest.
If you’re new to magnesium water, start with one or two glasses a day and increase gradually. People who are sensitive to magnesium’s bowel effects often do better spreading their intake across the day rather than drinking a large amount at once. If loose stools persist, reduce the concentration by using less magnesium hydroxide per liter.
Tips for a Better Result
- Use the coldest seltzer possible. Cold liquid holds more CO2, which means more gas available to react with the magnesium. Pulling the bottle straight from the fridge gives the best results.
- Don’t use flavored sparkling water. Added citric acid or other flavorings can interfere with the reaction or change the taste in unpleasant ways.
- Check that the water goes fully clear. Cloudiness means unreacted magnesium hydroxide is still suspended. This won’t hurt you, but it means you’re drinking a mild laxative rather than dissolved magnesium bicarbonate.
- Choose plain milk of magnesia. Many brands add flavoring, coloring, or inactive ingredients like bleach-based preservatives. Read the ingredient list and pick one where magnesium hydroxide and purified water are the only ingredients.
How It Compares to Supplements
Magnesium bicarbonate dissolved in water has a practical advantage over pills: it’s already in solution, so your body doesn’t need to break down a tablet first. Research on magnesium-rich mineral waters has found that magnesium from water is bioavailable, meaning your body absorbs it efficiently. The absorption happens gradually as you sip throughout the day, which also reduces the chance of digestive upset compared to taking a large dose from a single capsule.
The tradeoff is convenience. A magnesium supplement delivers a precise dose in seconds. Magnesium water requires a bit of preparation, takes up fridge space, and delivers its magnesium in a larger volume of liquid. For people who struggle with pill-based supplements or want to increase their water intake at the same time, it’s a practical alternative.