The most common way to remove magnesium from water is with a standard water softener, which swaps magnesium and calcium ions for sodium. But depending on how much magnesium you need to remove and why, several other methods work just as well or better. Here’s how each one works, what it costs, and what to consider before stripping this mineral from your supply.
Water Softeners (Ion Exchange)
A conventional salt-based water softener is the most popular home solution for magnesium removal. Inside the unit, resin beads carry a negative charge that attracts positively charged magnesium and calcium ions as water flows through. Those minerals stick to the resin, and sodium ions release into the water in their place. The resin periodically flushes itself with a salt brine solution, washing away the collected minerals and recharging the beads. Ion exchange resins can absorb more than 90% of the magnesium in your water.
A new whole-house water softener typically runs $2,100 to $2,600 installed. Ongoing costs are modest: you’ll buy salt regularly and budget a few hundred dollars a year for maintenance. This is the go-to option if your main concern is hard water problems like scale buildup in pipes, spotted dishes, or dry skin. The tradeoff is that your water’s sodium content increases, which matters if you’re on a low-sodium diet.
Reverse Osmosis Systems
Reverse osmosis (RO) pushes water through a semipermeable membrane with pores so small that dissolved minerals, including magnesium, can’t pass through. Standard RO membranes reject around 87% of magnesium, while tighter nanofiltration membranes can reach 95% rejection under the right conditions. RO doesn’t just target magnesium. It strips out virtually all dissolved solids, producing very pure water.
Most homeowners install an RO system under the kitchen sink to treat drinking and cooking water rather than the entire house. A point-of-use RO system costs $1,000 to $1,600 installed, including a storage tank and dedicated faucet. Filters and membranes need servicing every 12 to 18 months. If you want magnesium removed from every tap, whole-house RO systems exist but cost significantly more and waste more water in the process.
Distillation
Distillation is the most thorough method. Water is heated to steam, which rises and leaves dissolved minerals behind. The steam then cools and condenses back into liquid. Because magnesium doesn’t evaporate, it stays in the boiling chamber. A properly operated distiller removes up to 99.5% of impurities, including magnesium, calcium, iron, bacteria, and nitrates.
Countertop distillers are affordable to purchase but slow: most produce only about a gallon every four to six hours. They also use a fair amount of electricity to keep water at a boil. Distillation makes sense if you need very small quantities of mineral-free water, but it’s impractical as a whole-house solution.
Lime Softening (Municipal Scale)
If you’re dealing with magnesium removal at a larger scale, lime softening is the method water utilities use. Adding lime (calcium hydroxide) raises the water’s pH. At a pH above 10.6, dissolved magnesium converts to insoluble magnesium hydroxide, which forms solid particles that settle out or get filtered. Aggressive magnesium removal often requires pushing the pH to 11 or higher, a process called excess lime softening. Utilities sometimes add sodium carbonate (soda ash) alongside lime to supply extra carbonate ions that help pull calcium out at the same time.
This isn’t a DIY method. It requires precise chemical dosing, settling tanks, and pH adjustment afterward to bring the water back to a safe, drinkable range. But if you’re researching options for a well system, small community supply, or industrial application, lime softening is one of the most cost-effective approaches at volume.
Electrodialysis
Electrodialysis uses an electric current to pull charged mineral ions through specialized membranes, separating them from the water. It’s particularly effective for high-mineral or brackish water. In testing on concentrated brine water, electrodialysis systems achieved 93% to 98% magnesium removal depending on the voltage applied. At higher voltages, removal rates reached 98%.
This technology is used primarily in industrial and municipal settings rather than homes. It’s worth knowing about if you’re evaluating options for a commercial operation or a water source with extremely high mineral content where other methods might struggle.
Why Complete Removal May Not Be Ideal
Before you strip all the magnesium from your water, it’s worth understanding what you’d be giving up. Magnesium is an essential mineral, and while food is the primary source, drinking water provides a meaningful supplement that diet alone may not fully replace, even in countries with good nutrition.
Research on long-term consumption of demineralized water raises several concerns. Water low in magnesium has been associated with higher risks of cardiovascular disease, certain pregnancy complications like preeclampsia, and some neurological conditions. Hard water, by contrast, appears to carry a somewhat lower cardiovascular risk, with magnesium identified as the more likely contributor to that benefit.
There’s also a cooking factor many people overlook. When you use demineralized water to prepare food, it leaches minerals out of vegetables, meat, and grains. Losses can reach 60% for magnesium and calcium, with even steeper losses for trace minerals like copper and manganese.
If you’re removing magnesium to solve hard water problems like scale and soap scum, a whole-house softener paired with an unsoftened tap for drinking water gives you the best of both worlds. If you’re using RO or distillation for drinking water, adding a remineralization filter on the output side restores a healthy mineral balance. These small cartridges cost $20 to $50 and last several months.
Choosing the Right Method
- For whole-house hard water treatment: A salt-based water softener is the standard choice. It handles magnesium and calcium throughout your plumbing at a reasonable ongoing cost.
- For purified drinking water: An under-sink RO system removes magnesium along with other contaminants. Consider adding a remineralization stage.
- For maximum purity in small volumes: A countertop distiller removes 99.5% of dissolved minerals but produces water slowly.
- For large-scale or industrial use: Lime softening and electrodialysis are the most practical options, with electrodialysis excelling on high-mineral water sources.
Your water utility can tell you exactly how much magnesium your tap water contains, or you can order a home test kit for $15 to $30. Knowing your starting concentration helps you pick a method that matches the problem without over-treating your supply.