Reverse osmosis is the most reliable household method for substantially lowering TDS, typically reducing it to below about 50 ppm and stripping most dissolved minerals and many contaminants along the way. Distillation and deionization are recognized alternatives for specific situations, while activated carbon and most pitcher filters improve taste without meaningfully changing TDS. Dilution with a low-TDS source lowers the number but does not remove anything from the water.
If your goal is genuinely lower dissolved solids, the method matters more than the marketing. This guide walks through what TDS actually measures, why it matters at the kitchen sink, how each proven method works, and how to choose one based on your starting reading and daily volume.
What TDS Actually Measures
TDS stands for total dissolved solids, the combined weight of inorganic salts and a small amount of dissolved organic matter in a given volume of water. In typical US tap water, that includes calcium, magnesium, sodium and potassium, plus bicarbonates, chlorides and sulfates from natural sources and treatment, very small amounts of metals like iron, copper or zinc, and trace organic material.
The measurement itself is an estimate, not a contaminant test. Common household TDS meters are conductivity-based devices: they gauge how well the water conducts electricity and convert that into a reading, without identifying specific contaminants or distinguishing beneficial minerals from unwanted ones. A high or low value by itself does not tell you whether water meets local drinking water standards, so TDS is best treated as a general indicator of dissolved content rather than a direct measure of safety or contamination.
It also is not one substance. TDS is a sum, which is why a single number cannot tell you what is actually in the glass.
The 500 Mg/L Figure, Explained
In the United States, the EPA secondary standard for total dissolved solids is 500 mg/L. These National Secondary Drinking Water Standards set non-mandatory guidelines for 15 contaminants and are not enforced by the EPA. They exist for aesthetic reasons such as taste, color and odor, and the contaminants covered are not considered to present a health risk at those levels. EPA recommends them to water systems but does not require compliance, though individual states may adopt them as enforceable standards. You can review the EPA guidelines on drinking water for the broader regulatory context.
TDS has no primary maximum contaminant level because, at levels found in drinking water, it is not itself a health hazard; the 500 mg/L guideline protects taste, appearance and plumbing. That distinction matters: a reading above 500 mg/L is a reason to investigate what is driving it, not an automatic safety alarm.
A high reading is worth investigating because the minerals behind it, such as sodium or sulfate, can matter to some households, and because it can indicate naturally occurring contaminants in the same source. If you want a fuller explanation of the measurement itself, see What Does TDS Mean in Water?.
Why TDS Matters at the Kitchen Sink
Secondary contaminants cause three categories of problems: aesthetic effects such as undesirable tastes or odors, cosmetic effects that do not damage the body but are still unwanted, and technical effects such as damage to water equipment or reduced effectiveness of treatment for other contaminants. Those technical effects are where most kitchens feel TDS first.
Scale is the clearest example. Dissolved minerals precipitate out as deposits on heating elements, kettle interiors and coffee maker parts over time, which is exactly the kind of equipment damage the EPA category describes. That buildup is also why descaling matters for brewing equipment setup and for knowing how often you should clean a coffee maker.
For coffee and tea, water chemistry affects extraction. The Specialty Coffee Association publishes water standards for brewing, and coffee-science coverage of those standards describes target mineral windows for TDS, hardness and alkalinity. Treat those as indicative brewing targets rather than a regulatory standard, and note that they are secondhand figures. Check the SCA’s own published standards for the current exact values before relying on any specific number.
The practical upshot: lowering TDS addresses taste, scale and equipment wear. It is not the same task as making water safe, which depends on what specifically is in it.
Reverse Osmosis
Reverse osmosis forces water through a semi-permeable membrane that rejects dissolved solids, producing water with substantially reduced TDS, often below 50 ppm, with most dissolved minerals and many contaminants reduced. As a treatment option for taste and scale complaints, RO is one of the proven approaches alongside ion exchange and distillation.
The trade-off is reject water. Published figures for under-sink RO systems vary widely, and the ratio depends on water pressure, TDS level, temperature and system design. Because these figures come from commercially motivated sources and mix different ratio conventions, treat any single number as a typical range rather than a guarantee for your setup, and check the specifications of the specific system you are considering.
Maintenance directly affects both water quality and efficiency. Clogged prefilters, membrane aging, or delayed filter replacement can gradually reduce efficiency and increase wastewater output over time. That is the failure mode to watch: a system that still produces water but produces it more slowly and wastes more of it.
If the water is destined for coffee or espresso, some households blend or remineralize. Remineralized RO water has moderate TDS depending on the minerals intentionally reintroduced and is used for drinking and specialty beverage preparation. Filter choice also interacts with machine type, which is worth checking against reservoir-based machine specs before committing.
Distillation
Distillation is listed among the proven treatment options for taste and scale complaints. The evidence behind this guide does not provide a source for the specific separation mechanism, so treat the mechanism as a general description rather than a verified technical claim.
Two practical limits deserve honesty. Distillation is energy-intensive because it requires boiling, and it is slow compared to a plumbed RO system. Specific reduction percentages, energy figures and cycle times are not established in the evidence behind this guide, so treat manufacturer claims on those points as claims to verify rather than settled facts. If you generate distilled water for a coffee machine, plan on batch production rather than on-demand supply.
Deionization
Deionization passes water through ion-exchange resins that swap dissolved ions for others attached to the resin. Like distillation, it is recognized as a treatment option for taste and scale complaints.
DI is listed among the recognized treatment options for taste and scale complaints. The evidence behind this guide does not establish a specific scope limitation for DI, so treat any claim about its practical volume limits as a claim to verify against the specific system’s documentation. Resin regeneration and disposal procedures vary by product and are not covered by the evidence here, so follow the specific system’s instructions rather than a general rule.
Activated Carbon and Pitcher Filters
This is the most common source of disappointment, so it is worth being exact. Standard activated carbon is not a dependable fix for TDS or hardness. The evidence behind this guide does not establish a complete list of other contaminants that carbon cannot remove, so check the specific filter’s certification for the contaminants you care about.
Pitcher filters tell the same story with a nuance. From a TDS perspective, a pitcher filter can sometimes change the reading, but it may also leave TDS largely unchanged while still improving taste and odor. Some pitcher cartridges include ion-exchange resins that swap ions such as calcium, magnesium or certain metals for hydrogen, sodium or potassium attached to the resin. That can change the composition of what is dissolved and produce a small increase or decrease in measured TDS, depending on how many ions are exchanged and how the meter interprets conductivity.
In other words, a pitcher that drops your reading by 20 ppm has not necessarily removed 20 ppm of contaminants; it may have traded one ion for another. For the full breakdown of what different filter types can and cannot do, see Do Water Filters Remove TDS?.
Dilution and Blending
If you have access to a second, lower-TDS source, blending is a lower-cost partial fix. The proven options for taste and scale complaints include blending where a second, lower-TDS source is available. Blending is a partial fix, not a treatment method, because it changes concentration rather than composition.
Be clear about what blending does. It lowers the measured concentration by mixing, not by removing anything. If the higher-TDS source contains a contaminant you care about, blending reduces its concentration but does not eliminate it, and it dilutes your low-TDS source at the same time. Rainwater illustrates how variable a low-TDS source can be: fresh rain can contain only a few milligrams per liter of dissolved material, while roof-collected rainwater may measure several tens of milligrams per liter after picking up dust and salts. If you collect rainwater, test it rather than assuming a number.
Dilution makes sense when the only problem is a taste or scale complaint and you already have good low-TDS water on hand. It is the wrong tool when the goal is removing something specific.
Comparing the Methods
| Method | Typical TDS reduction | Speed and water use | Best fit | Main limitation | | |—|—|—|—|—| | Reverse osmosis | Substantially reduced, often below about 50 ppm | On-demand for plumbed systems; typically 3 to 4 gallons wasted per gallon purified for traditional units, closer to 1:1 for efficient designs under the right conditions | Households wanting substantial TDS reduction for drinking and cooking | Reject water and ongoing filter and membrane maintenance; efficiency drops with clogged prefilters or an aging membrane | | Distillation | Recognized treatment option; specific reduction not established here | Batch process, energy-intensive | Readers who want a proven treatment option and can accept energy and time costs | Energy use and slow production | | Deionization | Recognized treatment option; specific reduction not established here | Low-volume, cartridge-based | Specialized low-volume needs where very low mineral content is wanted | Resin regeneration and disposal handling | | Activated carbon and pitcher filters | Not a dependable fix for TDS; readings may barely move or shift slightly either way | Fast, no reject water | Better taste, odor and chlorine reduction rather than lower TDS | Does not meaningfully lower TDS, hardness or several dissolved contaminants | | Dilution and blending | Lowers the measured number by mixing only | Instant, no equipment | Readers with a second, lower-TDS source wanting a partial fix | Does not remove contaminants; concentration only |
Measuring TDS Correctly
Start with a baseline. Take a reading of your untreated supply before buying anything, because the method you need depends entirely on where you are starting. Remember that the meter is estimating conductivity, not identifying what is dissolved.
Then measure after treatment. A post-treatment reading tells you whether the system is doing what you expected, and for RO it doubles as an efficiency check: a rising post-treatment number alongside increasing wastewater is a signal of clogged prefilters or an aging membrane.
Keep the limits in view. Because a household meter cannot distinguish minerals from contaminants, a low reading does not prove the water is safe, and a high reading does not prove it is unsafe. The 500 mg/L figure is a non-enforceable US guideline for aesthetics, and other jurisdictions may set different limits. Neither a low nor a high reading on its own establishes anything about health.
Calibration procedures and temperature-correction coefficients vary by meter model and are not covered here. Follow your meter’s own instructions, and measure at a consistent temperature so you are comparing like with like rather than chasing drift.
Frequently Asked Questions
Does Boiling Water Lower TDS?
No. Boiling does not lower TDS. Distillation is a different process from simply boiling, and it is listed among the recognized treatment options for taste and scale complaints. The evidence behind this guide does not provide a source for the specific mechanism by which boiling and distillation differ, so treat that explanation as a general description rather than a verified technical claim.
Do Refrigerator and Pitcher Filters Lower TDS?
Usually not meaningfully. A pitcher filter may leave TDS largely unchanged while still improving taste and odor. If a cartridge includes ion-exchange resin, the reading can shift slightly in either direction as ions are swapped.
Why Does My Filtered Water Still Show High TDS?
Because most standard filters, including carbon filters, are not designed to remove dissolved solids. Standard carbon is not a dependable fix for TDS, hardness, nitrate, fluoride, arsenic or microorganisms. If you want a lower number, you need a method that actually removes dissolved content.
What Is a Normal TDS Reading?
There is no single normal. The US secondary guideline is 500 mg/L, a non-enforceable aesthetic standard, and secondary standards are not considered to present a health risk at those levels. Brewing targets are separate and stricter, and the SCA publishes its own water standards for coffee brewing. Check the SCA’s current published values rather than relying on secondhand summaries.
Can I Lower TDS Without Installing an RO System?
Yes, with caveats. Distillation and deionization are recognized options, and blending with a lower-TDS source lowers the measured number. What will not work is expecting a carbon or pitcher filter to do the job.
How Often Should I Replace RO Filters and Membranes?
Specific intervals are not established here and vary by system, water quality and usage. The signal to act on is performance: clogged prefilters, membrane aging, or delayed replacement gradually reduce efficiency and increase wastewater output. Track your post-treatment reading and reject-water volume rather than relying on a calendar alone.
Is Low-TDS Water Bad for You?
The evidence behind this guide does not establish health effects of low-mineral or near-zero-TDS drinking water, so no safety conclusion should be drawn from the TDS number alone. What the sources do establish is narrower: at levels found in drinking water, TDS is not itself a health hazard, which is why it has no primary standard and only an aesthetic guideline. If you want an authoritative answer on daily consumption of demineralized water, consult a public health authority such as the WHO or your local water regulator, because that question is outside what the sources here can settle.
Choosing the Right Approach
Work backward from three things: your starting reading, your daily volume, and what you actually want to fix.
If you need substantial TDS reduction for drinking and cooking at volume, reverse osmosis is the method the evidence supports, with the understanding that it produces reject water and needs regular filter and membrane attention. If your volume is small and specialized, deionization is a recognized option. If you want a proven treatment option and can absorb the energy and time cost, distillation fits.
If your complaint is taste and odor rather than scale or dissolved content, start with carbon filtration. It is not going to move the TDS number much, but taste and odor improvement is what it is actually good at. And if you already have a low-TDS source on hand, blending is a legitimate partial fix for a taste or scale complaint, as long as you accept that it dilutes rather than removes.
One last check before you buy: confirm what your reading actually represents. If you suspect a specific contamination problem rather than a general hardness or taste issue, a conductivity pen cannot answer that question, because it does not identify what is dissolved. For broader context on how TDS relates to health questions, see Is High TDS in Drinking Water Bad?.
