High TDS Levels in Water: Causes & What to Do

As a smart hydration specialist, I see one scenario over and over: someone buys a TDS meter, checks their drinking water or pool, and suddenly the number is way higher than before. The first reaction is usually panic. The good news is that a sudden jump in total dissolved solids (TDS) is rarely an immediate health emergency, but it is an important signal about what is happening in your water system.

This article walks you through what TDS really means, why it can spike suddenly, when that spike matters for health and equipment, and how to respond in a calm, science‑based way—whether you are managing a home hydration system, a private well, or a pool or spa.

TDS 101: What Those Numbers Actually Mean

Total dissolved solids are the sum of everything dissolved in your water that is not a water molecule. Research from organizations such as Ohio State University, KnowYourH2O, Fresh Water Systems, and others consistently define TDS as the combined concentration of minerals, salts, metals, and small organic substances dissolved in water. That includes common minerals like calcium, magnesium, sodium, potassium, and bicarbonates, as well as chloride, sulfate, nitrate, trace metals such as copper, zinc, and sometimes contaminants like pesticides or industrial byproducts.

TDS is usually reported in milligrams per liter (mg/L) or parts per million (ppm), and for practical purposes those units are interchangeable at household levels. A reading of 300 ppm means there are 300 parts of dissolved substances in one million parts of water. Most everyday water falls into one of three broad categories: low‑mineral water such as deionized water with very low TDS, typical drinking water in the low hundreds of ppm, and higher‑TDS water that tastes noticeably salty, bitter, or metallic.

Scientists and regulators emphasize that TDS is a broad indicator rather than a specific contaminant. The U.S. Environmental Protection Agency treats TDS as a secondary (aesthetic) parameter with a suggested upper level of about 500 mg/L in drinking water, based on taste, appearance, and technical issues like scaling rather than direct toxicity. Extension publications from Oklahoma State University and Montana State University echo this: high TDS makes water more likely to taste off, look murky, and irritate the digestive system for people not accustomed to it, but the number by itself does not tell you which substances are present or whether they are harmful.

At the same time, water‑quality guides from well‑water specialists such as CrystalQuest and DoctorFresh point out that TDS above roughly 500 mg/L can coincide with problematic levels of salts, nitrates, or heavy metals. They often recommend treatment at somewhat lower levels if you see scaling, appliance damage, or strong taste or odor changes. That is why a sudden jump in TDS deserves attention even if it does not automatically equal unsafe water.

To put the taste side in perspective, Waterdrop’s review of international guidelines summarizes a commonly used palatability scale for drinking water:

TDS range (mg/L)	Taste-based description (Waterdrop review)
<300	Excellent
300–600	Good
600–900	Fair
900–1200	Poor
>1200	Unacceptable for taste

In practice, I treat TDS as a dashboard gauge, not a diagnosis. It tells you when something about your water has changed and when it is time to look deeper.

Drinking Water vs Pools and Spas: Different Contexts, Same Physics

The meaning of a TDS spike depends on where you are measuring. For drinking water, the main concerns are taste, long‑term exposure to specific dissolved substances, and the impact on plumbing and appliances. For pools and spas, TDS is also tied to how well disinfectants work and how aggressive or scale‑forming the water is.

Pool chemistry experts at Orenda note that in pools and hot tubs, TDS is dominated by salts and minerals, especially sodium and calcium, along with chlorides, sulfates, alkalinity ions, nitrogen compounds, and various organics. Every chlorine product eventually turns into chloride, and products such as sodium bicarbonate, calcium chloride, and algaecides all leave behind dissolved residues. Orenda’s field work and industry articles argue that TDS itself is not usually the villain; rather, it affects the Langelier Saturation Index (LSI), which predicts whether water will dissolve calcium from surfaces or deposit it as scale.

Technical guidance from the International Code Council explains that as TDS rises, the LSI tends to fall, making water more aggressive and more likely to corrode metal fixtures and etch plaster if other factors are not adjusted. Pool standards often recommend keeping TDS no more than about 1,500 ppm above the starting level for that pool water. Because saltwater pools start with several thousand ppm of salt, their acceptable TDS range is correspondingly higher.

The physics is the same in your home plumbing. Studies and fact sheets from KnowYourH2O and others show that very low TDS water can be corrosive because it has little buffering capacity and tends to leach metals from pipes, whereas very high TDS water promotes scale and corrosion because it carries more ions, increases electrical conductivity, and drives mineral deposits. The difference is that in a pool you see those effects on tile lines and pool heaters, while in a kitchen you notice them as scale on your kettle, spots on glasses, and reduced appliance life.

A simple example helps connect the dots.

Imagine a backyard pool filled from tap water that starts at 300 ppm TDS. Over a hot season, the pool evaporates several feet of water. Each inch that evaporates leaves dissolved solids behind and is replaced with fresh water, which brings in more minerals and salts. Orenda reports that in hot, arid climates, outdoor pools can lose 8 to 10 feet of water annually to evaporation. If you do not drain or dilute, the TDS can roughly double in a year, purely from evaporation and refilling, even before you count chemical additions. The same concentration mechanism affects decorative fountains, humidifiers, and even small countertop kettles.

Why TDS Usually Changes Slowly—And What Can Make It Jump

Laboratory and extension publications from Montana State University and others point out that alkalinity, pH, and TDS in groundwater tend to be relatively stable over time. When you see a sudden change on your TDS meter, it usually means one of three things: the source water changed, human activity introduced new dissolved solids, or the measurement itself is off.

Natural and Seasonal Drivers

Total dissolved solids often rise after heavy rains, snowmelt, or drought, especially in private wells and small systems. Ohio State University and KnowYourH2O describe how TDS in groundwater reflects the minerals and salts that water has picked up from rocks and soil, such as calcium, magnesium, sodium, bicarbonate, sulfate, and chloride. When stormwater or irrigation water carries fertilizers, manure, or road de‑icing salts into the subsurface, those additional ions can push TDS up significantly.

CrystalQuest’s guide to well water TDS notes that wells drawing from mineral‑rich bedrock such as limestone or gypsum naturally have higher baseline TDS. It also highlights agricultural runoff, saltwater intrusion in coastal areas, and road salt as common causes of elevated TDS in wells. After a big spring thaw near a salted roadway or a heavy fertilizer application, it is normal to see a well’s TDS jump from what CrystalQuest would call a “good” range (around 150–300 mg/L) into the “acceptable but taste‑affected” range (300–500 mg/L) or higher in a relatively short time.

Even municipal surface water sources can experience seasonal swings when rivers receive more runoff carrying salts and nutrients.

While large utilities are required to manage these changes, homeowners on private wells need to monitor on their own and retest whenever they notice sudden changes in taste, odor, or appearance, as Ohio State University and KnowYourH2O both recommend.

Human Activities and Plumbing Effects

High TDS often traces back to everyday human activities. Environmental and consumer guides from Briowater, Trity Enviro, and KnowYourH2O describe several recurring patterns. Agricultural runoff brings in nitrates, phosphates, and other fertilizer components. Industrial discharges, if not properly treated, can release heavy metals and synthetic chemicals. Municipal disinfection adds chlorine and other treatment chemicals. Household products, from detergents to cleaning agents, can seep into local water bodies if wastewater is not effectively managed.

Inside the home, piping and water‑treatment equipment can also shift TDS quickly. When corrosive water—often lower in pH or with very low TDS and alkalinity—flows through metal plumbing, it can dissolve copper, zinc, lead, and iron, raising TDS and leaving metallic tastes. Montana State University notes that water with pH below about 6.5 is more likely to be corrosive and recommends testing for metals such as lead and copper in that case.

Water softeners are another frequent source of TDS shifts. KnowYourH2O and Ohio State University emphasize that softeners do not reduce total dissolved solids; instead, they exchange calcium and magnesium for sodium or potassium. The softness improves feel and reduces scaling, but the total ion load often stays similar or nudges upward. That is why a home that installs a softener may suddenly see TDS readings rise even though hardness and visual scale decline. A salty taste after softening can indicate elevated sodium and chloride from that exchange process or a softener that is not regenerating correctly.

Treatment and Operational Changes

Any time you modify how water is treated, you should expect TDS to respond. Pool‑chemistry articles from Orenda demonstrate vividly how dose decisions affect TDS. Liquid chlorine leaves sodium and chloride behind. Cal‑hypo adds calcium and chloride, roughly 4 ppm of calcium for every pound in 10,000 gallons of pool water. Dichlor and trichlor both contribute cyanuric acid and chloride. Sodium bicarbonate and sodium carbonate raise alkalinity and sodium. Calcium chloride adds both calcium and chloride. Each product does the job it is intended to do, but all of them also raise TDS step by step.

Something similar happens with drinking‑water systems. Reverse osmosis (RO) units, which employ a semipermeable membrane to reject most dissolved ions, normally reduce TDS by roughly 90–99 percent according to sources such as CrystalQuest, DoctorFresh, and Fresh Water Systems. Fresh Water Systems even uses a concrete example: with feed water at 260 ppm and RO water at 20 ppm, the system is achieving about 92 percent TDS rejection. If you have been measuring consistently low TDS at your RO faucet and suddenly the reading climbs from around 20 ppm to 80 ppm while the incoming tap water has not changed, that is often a sign that the membrane is fouling or nearing the end of its life.

I routinely use this pattern in my own field work. When an under‑sink RO system is installed, I log both feed and product TDS. As long as the rejection percentage stays in that typical 90–99 percent band, I know the membrane is doing its job. When the product TDS starts creeping up even though feed TDS remains similar, I know it is time to take a closer look at prefilters, pressure, and membrane condition.

Is a Sudden TDS Spike a Health Emergency?

Most regulatory and educational sources treat TDS as a technical and aesthetic concern, not a direct health standard. The EPA’s secondary drinking water guideline of 500 mg/L is based on taste and appearance, not toxicity. Canadian guidelines, summarized by Safe Drinking Water Foundation, also treat TDS as an aesthetic parameter at around 500 mg/L, although some provinces with naturally high‑TDS water set more lenient guidance, such as 1,500 mg/L in parts of Saskatchewan.

Ohio State University and KnowYourH2O both emphasize that elevated TDS alone does not prove that water is unsafe. However, they also caution that high TDS can signal that other primary contaminants—such as nitrate, arsenic, or lead—are present, especially where human pollution or corrosive conditions exist. Well‑water guidance from CrystalQuest frames TDS above about 500 ppm as a trigger to investigate further, particularly if there are taste, odor, or scaling problems.

On the other end of the spectrum, some water‑treatment providers take a more aggressive stance. Water Pros in Colorado, for example, argue that even seemingly harmless minerals like calcium and magnesium can build up in the body and prefer drinking water with TDS in the 50–150 ppm range rather than the 500 ppm allowed by EPA’s aesthetic standard. DoctorFresh cites guidance that calls 50–150 mg/L “excellent,” 150–250 “good,” 250–500 “acceptable,” and water above roughly 900–1200 mg/L unsafe for drinking, particularly where potentially harmful ions are involved.

The science‑based middle ground looks like this. A sudden TDS jump is not usually an emergency, but it is a clear signal to ask two questions: how far did it move, and what could be driving that change where I live? If your city water shifts from 250 to 400 ppm and still tastes fine, that may be within seasonal or blending variability, though you can always request a water‑quality report. If a rural well jumps from 250 to 800 ppm after heavy fertilizer use nearby, or if you see a big increase along with new salty or metallic tastes, that pattern deserves a full lab workup focused on nitrates, metals, and other likely contributors, as recommended by well‑water guides from Ohio State University and CrystalQuest.

How to Verify a Sudden TDS Change

Before you redesign your treatment system or drain a pool, it is worth confirming that the TDS change is real and not just a testing artifact. Almost every source, from Orenda to Culligan to DoctorFresh, stresses that measurement tools for TDS have limitations and require careful use.

Step One: Check the Measurement, Not Just the Number

Most consumer TDS meters are actually conductivity meters that estimate TDS from how well the water conducts electricity. They send a small electrical current through the sample, measure conductivity, and then apply a conversion factor. Oklahoma State University notes that for many household waters, TDS in mg/L is roughly 0.66 times the electrical conductivity expressed in micromhos per centimeter. That means water with conductivity of 500 micromhos per centimeter would have an estimated TDS near 330 mg/L.

Because TDS meters rely on that indirect relationship, their accuracy depends on the right conversion factor for your water and regular calibration. Articles from Orenda and DoctorFresh highlight that proper maintenance and periodic calibration are critical. When a homeowner tells me their TDS “suddenly” doubled in a day, my first step is always to: retest the same tap with a freshly rinsed meter, test a second sample taken a few minutes later, and, if possible, compare with a second meter or a calibrated standard solution. Very often the first shock reading came from a dry probe, trapped air bubbles, or a meter that has drifted.

TDS test strips are another quick tool. They change color based on ion strength and can tell you whether TDS is roughly low, medium, or high, but they are less precise than a good electronic meter. For precise decisions, especially on wells, laboratory gravimetric methods—where a measured volume of water is evaporated and the mass of remaining solids is weighed—are still the reference standard. DoctorFresh describes this method and even gives an example calculation using a 50 milliliter sample and a measured mass difference to compute mg/L TDS.

Step Two: Pair TDS with Other Clues

TDS does not operate in isolation. Water‑quality panels from Oklahoma State University’s household testing program and Montana State University’s well‑water resources include TDS alongside pH, hardness, calcium, magnesium, sodium, chloride, sulfate, nitrate, iron, and other key parameters. The combination tells a much richer story than any single number.

If TDS has jumped and you also see higher nitrate, that points toward agriculture or septic issues. If TDS has risen along with sodium and chloride after installing or adjusting a softener, that aligns with the expected sodium exchange process. If TDS is high and pH is low, Montana State University suggests that corrosion potential increases and testing for metals such as lead and copper becomes important.

Your own senses are useful too. The Level 1 diagnostic approach outlined by KnowYourH2O encourages paying attention to salty, metallic, or bitter tastes, discoloration, and odors such as mustiness or sulfur. A new salty taste along with a TDS jump is very different from a TDS change with no sensory differences.

Step Three: Decide When to Order Professional Analysis

Well‑water guides from CrystalQuest and Ohio State University recommend using a low‑cost digital TDS meter monthly and obtaining a certified laboratory analysis annually or whenever taste, odor, or appearance changes. In my own practice, I encourage that schedule for private wells that show moderate or high TDS, have nearby agriculture or industry, or serve vulnerable populations such as infants and pregnant women.

For municipal water, it is reasonable to rely on the utility’s routine testing, but if your TDS meter shows a sustained shift combined with new tastes or stains, I suggest either requesting the latest utility report or arranging an independent test that includes TDS, major ions, nitrate, and metals. Companies such as Culligan point out that a professional in‑home test can also check hardness, chlorine, and common nuisance issues in about half an hour, which can be a pragmatic way to get context for your TDS readings.

Practical Strategies to Manage High or Rising TDS

Once you have confirmed that a TDS increase is real and understand the likely contributors, you can choose the right management approach. Because TDS is a sum of many substances, you match the solution to the problem: reverse osmosis, distillation, deionization, or sometimes simply partial dilution.

Drinking Water and Whole‑Home Hydration Systems

For drinking water, the goal is clean, good‑tasting water that supports hydration and protects your plumbing and appliances. Several technologies reduce TDS effectively.

Reverse osmosis systems push water through a semipermeable membrane that blocks most dissolved ions. Briowater, Fresh Water Systems, CrystalQuest, and DoctorFresh all highlight RO as one of the most comprehensive home options, typically removing about 90–99 percent of TDS, including salts, fluoride, arsenic, and many other contaminants. Fresh Water Systems uses the TDS rejection percentage as a performance metric; for example, dropping feed TDS from 260 ppm to 20 ppm represents more than 90 percent removal.

Distillation, described in multiple consumer guides, removes TDS by boiling water and condensing the steam so that salts and minerals remain behind. Deionization systems use ion‑exchange resins to swap them out of the water. Both can produce near‑zero‑TDS water, which is valuable for laboratories, aquariums, or spot‑free rinsing. However, KnowYourH2O and Safe Drinking Water Foundation caution that very low TDS water can taste flat, be more corrosive to metal plumbing, and in the long run encourage higher levels of trace metals if not managed properly. That is why many home hydration systems use RO followed by remineralization, passing the water through a magnesium and calcium media to restore some minerals, improve taste, and stabilize pH before the water reaches your glass.

It is also important to understand what traditional water softeners do and do not do. Ohio State University and Fresh Water Systems make it clear that softeners remove hardness (mainly calcium and magnesium) but do not lower total dissolved solids; in fact, they often increase sodium in the water. If your TDS spike is primarily due to hardness minerals and you are dealing with scale on fixtures and short‑lived heaters, a softener may be the right tool. If you want to reduce the total level of dissolved salts for taste, appliance protection, or specific contaminants, you need RO, distillation, or deionization.

In a typical home project, when I see feed water with TDS around 700–800 mg/L, noticeable scale, and a slightly bitter taste, I often pair a whole‑house softener for hardness control with a point‑of‑use RO system at the kitchen sink for drinking and cooking. The softener protects plumbing and appliances, while the RO unit drops TDS at the glass to well under 100 mg/L, which aligns with the “excellent” band described in several drinking water guidelines.

Private Wells

Well owners shoulder more responsibility because private wells are usually not regulated or monitored by government agencies. CrystalQuest emphasizes that homeowners must test and manage TDS themselves, noting that 0–50 ppm is rare in wells and more typical ranges are 50–150 ppm (excellent), 150–300 (good), 300–500 (acceptable but taste may be affected), and more than 500 (potentially unsafe; treatment recommended).

For wells with TDS just above 500 mg/L but no specific contaminants identified, you may choose to treat only drinking and cooking water with a point‑of‑use RO system. When TDS is higher, when harmful ions such as nitrates or arsenic are present, or when scale and corrosion are affecting the whole house, CrystalQuest recommends whole‑house RO systems. These require careful design for the well’s pressure, flow, and prefiltration needs, especially where iron or sediment is present. They often incorporate storage tanks and sometimes booster pumps if well pressure is below about 40 psi.

At higher TDS levels, appliances can suffer. CrystalQuest estimates that water heaters, dishwashers, and washing machines operating on water above roughly 500 ppm TDS may see a 30–50 percent reduction in service life compared with those using treated water. In my own field visits, I have opened heaters caked with scale that accumulated because TDS and hardness were ignored for years.

Investing in treatment up front often costs less than serially replacing equipment.

Pools, Spas, and Hot Tubs

For pools and spas, TDS management is less about direct health effects and more about water balance, sanitizer performance, and protecting surfaces and equipment. Orenda and the International Code Council both emphasize that TDS is now higher in many pools than in past decades because of salt systems, higher chemical use, and water‑use restrictions that limit draining.

TDS is one of the factors in the Langelier Saturation Index, alongside pH, alkalinity, calcium hardness, temperature, and cyanuric acid. Higher TDS reduces the LSI, making water more aggressive if you do not adjust the other parameters. According to the International Code Council, recommended practice is to test TDS regularly and to keep pool and spa TDS within about 1,500 ppm of the starting level, which includes both balanced water and any initial salt added. For spas, they suggest fully draining the water when TDS exceeds the source water by 1,500 ppm or when a calculated water replacement interval is reached, whichever comes first.

When TDS is too high, the simplest fix is usually partial drainage and dilution with lower‑TDS water. Orenda and other industry resources also mention reverse osmosis filtration for pools in regions facing drought or water restrictions, which can significantly lower TDS without draining the entire vessel. Chemical products like clarifiers may improve clarity but do not remove TDS; they just shift particles around.

In practice, I look at TDS in a pool or spa as a proxy for water “age.” When TDS is steadily climbing, more chemicals are needed to maintain balance, surfaces begin to show stubborn scale or etching, or sanitizer efficiency drops, that is the point where a controlled drain‑and‑refill or RO treatment becomes a smart investment in clarity, comfort, and equipment life.

Building a Smart TDS Monitoring Routine

Modern water‑quality monitoring is moving quickly from occasional lab samples to continuous sensing. Reviews of sensing technologies in journals and industry overviews describe how conductivity and TDS sensors can be integrated with Internet‑connected monitoring systems to provide real‑time data on water quality. AlpHa Measurement Solutions, for instance, manufactures inline conductivity‑based TDS probes that handle a wide range of conductivities and temperatures and can feed pool‑management or industrial systems.

Even at the home scale, there are practical ways to set up a simple TDS monitoring routine. For private wells, CrystalQuest recommends monthly checks with a handheld TDS meter and a comprehensive lab test once a year. For homes with RO systems, Fresh Water Systems suggests using TDS readings to track membrane rejection percentage over time. When feed TDS is stable but post‑filter TDS rises, it is time to inspect or replace filters.

In my own design work, I like to create a three‑point snapshot: measure TDS at the source (well or incoming municipal line), after any whole‑house treatment such as softening, and at the drinking water point of use. Over a few months, that simple habit builds a profile of how your water behaves seasonally, how treatment is performing, and when changes are meaningful.

The key is to remember that TDS is one piece of a fuller picture. Data from continuous monitoring studies, summarized in systematic reviews of water‑quality sensing, show that combining TDS or conductivity with pH, temperature, turbidity, and sometimes chlorine or dissolved oxygen gives a much richer and more reliable view of water health than any single parameter alone.

Short FAQ: Everyday Questions About TDS Spikes

Q: Can low TDS be a problem, or is lower always better? Very low TDS water (for example, deionized water under about 50 mg/L) can taste flat and, according to KnowYourH2O and Safe Drinking Water Foundation, can be more corrosive to plumbing, leaching metals like copper and lead. There is no consensus that such water is harmful to healthy adults in the short term, but from a smart hydration and home‑systems standpoint, I rarely aim for zero TDS. I prefer to remove unwanted ions and then remineralize slightly so the water is stable, tastes good, and is gentle on pipes.

Q: Does a water softener reduce TDS? No. Softening targets hardness minerals—mainly calcium and magnesium—but does not reduce the overall amount of dissolved solids. In fact, softeners usually increase sodium or potassium in the water because they swap hardness ions for those. Extension resources from Ohio State University and technical notes from Fresh Water Systems both stress that you should not use a softener to manage TDS. If TDS is high and you want to lower it, you need technologies such as reverse osmosis, distillation, or deionization.

Q: How often should I check TDS? For private wells, CrystalQuest advises using a digital TDS meter monthly and getting a comprehensive laboratory test annually. For city water, it is reasonable to spot‑check TDS occasionally and anytime you notice changes in taste, odor, or staining, as suggested by Ohio State University and KnowYourH2O. For RO systems, I often recommend checking TDS at the RO faucet monthly so you can spot membrane performance changes early. Pools and spas benefit from at least monthly TDS checks in residential settings and more frequent checks in heavily used commercial facilities, according to pool‑industry guidance.

As a smart hydration specialist, I see TDS as one of the most useful early‑warning signals you can have. When you understand what drives sudden increases, how to verify them, and how to respond with the right mix of testing and treatment, you can turn a scary‑looking number on a meter into a practical tool for protecting your health, your hydration habits, and every piece of equipment your water touches.

References

About the author

Dr. Elena Brooks

Certified Water Quality SpecialistEnvironmental ScientistSmart Home Wellness Advocate

Environmental scientist turned smart home expert. Elena decodes the science of hydration to help modern families choose technology that supports long-term health.

Understanding Sudden Increases in TDS Levels for Water Quality Management