Several methods can effectively reduce total dissolved solids (TDS) in water without reverse osmosis, including distillation, deionization, nanofiltration, and electrodialysis. The right choice depends on how much water you need, your starting TDS level, and your budget. One common approach that does not work: boiling. Boiling actually concentrates dissolved minerals as water evaporates, raising TDS rather than lowering it.
Why Boiling Makes TDS Worse
This is worth addressing first because it’s the most intuitive guess and the most common mistake. When you boil water, pure water leaves as steam while the dissolved minerals stay behind in a shrinking volume of liquid. A study testing household purification methods found that none of the boiling tests produced TDS readings lower than the original value. Extended boiling for over 10 minutes concentrated the minerals so much that TDS jumped by roughly 300 ppm, potentially making the water less safe to drink. Boiling is excellent for killing bacteria and parasites, but it does the opposite of what you want for TDS.
Distillation
Distillation is essentially boiling done right. Instead of discarding the steam, you capture and condense it back into liquid water. Because dissolved minerals don’t evaporate with the water, the condensed output is nearly pure. Distilled water typically falls well below 500 mg/L TDS, which is the upper limit for drinking water set by most standards. Home countertop distillers are widely available and produce about 1 gallon every 4 to 6 hours.
The main limitations are speed and energy cost. Distillation uses a significant amount of electricity to keep water at a boil for hours, and output is slow compared to a tap-connected filter. It also strips beneficial minerals along with harmful ones, leaving flat-tasting water. For drinking purposes, some people add a small amount of mineral drops back in. Solar stills offer a lower-energy alternative, though they produce less water. Modified solar distillers using vertical wicks can boost output by 84 to 107% over basic designs, but even improved versions are best suited for small-scale or off-grid use.
Deionization (Ion Exchange Resins)
Deionization passes water through beds of specialized resin beads that swap dissolved mineral ions for hydrogen and hydroxyl ions, which combine to form pure water. Cation resins capture positively charged minerals like calcium, magnesium, and sodium. Anion resins capture negatively charged ones like chloride, sulfate, and nitrate. The result is water with extremely low TDS, often measured in fractions of a part per million.
Deionization systems come in cartridge form that connects to your water line. They work fast and produce high-purity water on demand, which is a major advantage over distillation. The trade-off is that resin cartridges exhaust over time and need replacement or regeneration, and the higher your starting TDS, the faster they wear out. For water above roughly 500 to 1,000 ppm TDS, cartridge life drops significantly, making ongoing costs higher. This is why deionization is most cost-effective as a polishing step after some initial TDS reduction, or when your source water has only moderately elevated TDS.
Deionized water is categorized into purity grades. Type III (purified) water has a resistivity above 0.05 megohms, suitable for general lab work and many household purposes. Type II and Type I reach progressively higher purity levels that are overkill for drinking but important for laboratory or industrial applications.
Nanofiltration Membranes
Nanofiltration uses a membrane similar to reverse osmosis but with slightly larger pores, operating at lower pressure and using less energy. It’s sometimes called a “loose RO” membrane. In brackish water testing, nanofiltration achieved about 43% TDS rejection on its own. That’s considerably less than RO’s 60% rejection in the same study, but it may be enough if your goal is to bring moderately high TDS down into a comfortable drinking range rather than stripping water to near-zero minerals.
Nanofiltration is particularly effective at removing divalent ions, the ones responsible for water hardness (calcium and magnesium), while letting more monovalent ions like sodium pass through. This selective filtering means it’s a strong choice if hardness minerals are the main contributor to your high TDS. Whole-house nanofiltration systems exist, though they’re more common in commercial settings. Point-of-use units for kitchen sinks are becoming more available and operate at lower pressures than RO, which can mean lower water waste.
Electrodialysis
Electrodialysis uses an electric current to pull dissolved ions out of water through ion-selective membranes. It’s a fundamentally different approach from pressure-driven filtration. The technology is proven at scale: in controlled testing, electrodialysis reduced water with 6,764 mg/L TDS down to 425 mg/L, a 94% removal rate at 18 volts. Even at lower voltages, removal rates of 59 to 83% were recorded.
Electrodialysis reversal (EDR) is a version that periodically switches the direction of the electrical current, which helps prevent membrane fouling and extends system life. EDR systems have demonstrated the ability to reduce TDS from over 29,000 mg/L down to roughly 1,700 mg/L. These are industrial-scale numbers, but smaller point-of-use electrodialysis units are entering the residential market. They tend to cost more upfront than cartridge-based options but have lower ongoing consumable costs since the membranes last longer than disposable filters or resin cartridges.
Lime Softening (Chemical Precipitation)
If your high TDS is driven primarily by calcium and magnesium (hard water), lime softening can help. This process raises the water’s pH high enough to force calcium carbonate and magnesium hydroxide out of solution as solid particles, which then settle out or get filtered. For water where hardness is the dominant component of TDS, this can meaningfully lower your reading.
Lime softening is more common in municipal treatment than in home setups, but it illustrates an important point: the composition of your TDS matters. A TDS meter gives you one number, but that number could represent calcium, sodium, iron, sulfates, or dozens of other dissolved substances. Knowing what’s actually in your water (through a basic water quality report from your utility or a home test kit) helps you pick the right method. If calcium and magnesium are the culprits, even a standard water softener using salt-based ion exchange will reduce those specific minerals, though it replaces them with sodium, so total TDS may not drop dramatically on the meter.
Activated Carbon Filters
Standard activated carbon filters, the type found in pitcher filters and refrigerator filters, are not primarily designed for TDS reduction. Their strength is removing chlorine, organic chemicals, and compounds that affect taste and odor. However, specialized activated carbon can achieve meaningful TDS reduction under the right conditions. Research using activated carbon derived from coffee husks achieved 72.73% TDS removal from industrial wastewater, outperforming some commercial activated carbon products.
For typical home use, a basic carbon filter alone won’t bring high-TDS water into an acceptable range. But if your TDS is only slightly elevated, or if the dissolved solids in your water include organic compounds rather than just minerals, carbon filtration can make a noticeable difference. It works well as a pre-treatment stage paired with another method like deionization.
Choosing the Right Method
Your starting TDS level is the single biggest factor in picking an approach. For water in the 500 to 1,000 ppm range, a deionization cartridge or nanofiltration unit can bring levels down to a comfortable drinking range without excessive cost. For water above 1,000 ppm, distillation or electrodialysis will handle the heavier lifting more reliably.
- Lowest upfront cost: A countertop water distiller (typically $80 to $250) handles small daily volumes effectively.
- Fastest output: Deionization cartridges produce purified water on demand at tap pressure, no waiting.
- Best for hard water specifically: Nanofiltration targets the divalent ions behind hardness and scale.
- Best for very high TDS: Electrodialysis systems can handle extremely mineral-heavy water, reducing TDS by 90% or more.
Combining methods often gives the best results. A carbon pre-filter to remove chlorine and organics, followed by a deionization cartridge, can produce very clean water from a moderately elevated source without any RO membrane involved. Testing your water before and after with an inexpensive TDS meter (under $20) lets you confirm your system is performing and tells you when filters or resin cartridges need replacement.