How to Reduce TDS in Water: Methods That Work
Mike Martin brings hands-on installation experience and helps validate the real-world setup and serviceability of the systems we cover.
✅ Quick answer: Reverse osmosis is the most practical way to reduce TDS in household drinking water. Mixed-bed ion exchange, distillation, and deionization can also remove dissolved solids. Ordinary carbon filters, sediment filters, water softeners, and boiling don’t lower TDS.
Test what makes up the TDS before choosing treatment. The number measures dissolved ionic content as a group. It doesn’t tell you whether the water contains harmless minerals, sodium, nitrate, arsenic, lead, or another specific substance.
Methods that reduce TDS
| Treatment | Reduces TDS? | Best fit |
|---|---|---|
| Reverse osmosis | Yes | Drinking and cooking water at a dedicated tap |
| Mixed-bed ion exchange | Yes | Small drinking-water volumes when frequent cartridge replacement is acceptable |
| Distillation | Yes | Small batches where slow production and energy use are acceptable |
| Deionization | Yes | Specialty high-purity applications, usually after other treatment |
| Lower-TDS source blending | Yes, by dilution | Cases with a verified alternate supply and controlled mixing |
| Water softener | No | Removing hardness through ion exchange |
| Carbon filter | No meaningful reduction | Specific chemicals, tastes, odors, and disinfectants |
| Sediment filter | No | Suspended sand, silt, rust, and other particles |
| Boiling | No | Kills susceptible germs but leaves dissolved solids behind |
The treatment should match the reason for the reading. If hardness is the problem, soften the water. If sodium, chloride, nitrate, or a mixture of dissolved ions needs reducing at the kitchen tap, RO or mixed-bed ion exchange may be the better fit.
🧪 What our TDS testing found
We’ve measured TDS across reverse osmosis, mixed-bed ion exchange, softening, and whole-house carbon treatment. The results show why a lower reading is a technology-specific outcome, not a universal score for filter quality.
| QWL test | Before | After | What it shows |
|---|---|---|---|
| Waterdrop G3P800 RO | 187 ppm | 28 ppm | 85% reduction after RO with fresh filters and membrane |
| ZeroWater pitcher | 187 ppm | Not detected by the lab | The included meter read 0–11 ppm across separate runs |
| Whirlpool WHES40E softener | 340 ppm | 350 ppm | TDS stayed similar while hardness fell from 18 to 1.6 gpg |
| SpringWell CF1 carbon system | 187 ppm in 2022 | 280 ppm in 2025 | The system wasn’t designed to lower TDS; the multi-year difference reflects source-water variation |
The RO and ZeroWater results are direct reduction examples using different technologies. The softener result shows that not every form of ion exchange lowers the total. The carbon result explains why TDS shouldn’t be used to grade a filter designed for different contaminants.
See the complete Waterdrop G3P800 lab results, ZeroWater pitcher test, Whirlpool WHES40E test, and SpringWell CF1 test.
What TDS actually measures
Total dissolved solids is the combined concentration of dissolved substances in water, commonly reported in milligrams per liter or parts per million. Calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica often make up much of the total.
A TDS number doesn’t identify those constituents. Two samples can both read 400 ppm while having very different chemistry and treatment needs.
The EPA lists 500 mg/L as a non-enforceable secondary guideline associated with aesthetic effects such as deposits, staining, color, hardness, or salty taste. It isn’t a federal health-based limit for TDS itself. WHO likewise doesn’t establish a health-based guideline value for total dissolved solids.
Does high TDS mean water is unsafe?
Not by itself. A high result can come from ordinary mineral salts, but a low result doesn’t prove that water is free from lead, PFAS, pesticides, microbes, or other contaminants.
Investigate when the number changes suddenly, exceeds the normal range for the source, accompanies salty or bitter taste, or appears with a known contamination event. Laboratory testing can identify the ions behind the total.
Turbidity and TDS are also different. Cloudy water contains suspended material or bubbles; dissolved ions are normally invisible. A sediment filter can clear particles without moving the TDS reading.
Does a water softener reduce TDS?
No. A conventional softener exchanges calcium and magnesium ions for sodium ions. The hardness drops, but dissolved material remains in the water in a different ionic form.
That’s exactly what our Whirlpool WHES40E test showed. Hardness dropped by 91%, while TDS changed only from 340 to 350 ppm, which is effectively similar given normal source variation.
If the goal is preventing hardness scale, a softener can succeed without lowering TDS. If the goal is lower dissolved sodium or chloride in drinking water, use a treatment designed for those ions, such as RO.
Does boiling water reduce TDS?
No. Boiling turns some of the water into vapor while dissolved salts remain in the container. As water evaporates, the concentration can rise.
Distillation is different because it captures the vapor and condenses it in a separate clean chamber. The original boiling container retains most nonvolatile dissolved solids.
How to reduce TDS without reverse osmosis
For household use, the alternatives are more limited:
- Mixed-bed ion exchange: Our ZeroWater pitcher sample went from 187 ppm to not detected in the lab. The included meter read 0–11 ppm across separate runs, but cartridge life can be short when incoming TDS is high.
- Distillation: Produces low-TDS water in batches but is slower and uses electricity.
- Deionization: Removes charged ions effectively but requires monitored resin and is generally used for specialty water, aquariums, laboratories, or as part of a larger purification train.
- Source blending: Dilutes high-TDS water with a tested lower-TDS supply. Safe blending requires knowing the chemistry of both sources.
- Source replacement: In severe well-water cases, a different aquifer, well modification, or delivered supply may be more practical than whole-house desalination.
Carbon, ceramic, KDF, ultrafiltration, and ordinary sediment cartridges may solve other problems, but they shouldn’t be sold as broad TDS-reduction technologies.
How to reduce TDS in well water
Start with a laboratory analysis rather than a meter alone. High well-water TDS may be driven by hardness, sodium, chloride, sulfate, nitrate, or another combination that changes the correct treatment.
- Identify the dissolved constituents. Include hardness, alkalinity, sodium, chloride, sulfate, nitrate, and any locally relevant contaminants.
- Treat the actual problem. Use softening for hardness, contaminant-specific treatment where appropriate, or RO for broad ionic reduction.
- Choose treatment location. Point-of-use RO is usually more practical when only drinking water needs low TDS.
- Engineer whole-house RO carefully. It requires adequate pretreatment, storage, pumping, reject-water planning, and post-treatment when necessary.
A high-TDS well doesn’t automatically need every dissolved mineral removed from every faucet. Treating drinking water separately can lower cost and wastewater production.
TDS meter vs. laboratory test
A handheld meter measures electrical conductivity and converts it into an estimated TDS value. It’s useful for tracking a stable source or calculating approximate RO reduction, but it can’t tell you which ions are present.
Use a laboratory test when selecting treatment or investigating an unexpected change. Use a meter afterward to monitor trends between lab tests. Our guide to using and interpreting a TDS meter owns the detailed measurement process.
Choosing the right treatment
- Lower TDS for drinking: Compare QWL’s lab-tested reverse osmosis systems or the lab-tested pitcher comparison.
- Unknown source of TDS: Start with the water-testing hub.
- Hardness and scale: Compare water softeners without expecting a lower TDS number.
- Other filter goals: Use the main water-filter hub to match the system to the contaminant and installation type.
The goal isn’t the lowest possible number. It’s to identify what the dissolved solids are, remove the substances that matter, and verify that the selected treatment is doing its intended job.
Sources: EPA secondary drinking-water standards, WHO total dissolved solids fact sheet, and USGS dissolved-solids guidance.