Think about the water from your faucet. No matter how pure it might seem, it may contain more than just H2O molecules. Water is an excellent solvent, meaning it readily dissolves particles from various compounds. These dissolved solids influence how the water tastes, smells, and appears, as well as its mineral content and safety. This is where TDS comes into focus.

This guide explains everything you need to know about TDS in tap water: what it is, how it is measured, how to manage levels in your water supply, and much more.

What is TDS?

Short for “Total Dissolved Solids,” TDS refers to the combined total of organic and inorganic compounds dissolved in drinking water, usually measured in milligrams per liter (mg/L), which is equivalent to parts per million (ppm). Importantly, TDS does not indicate what compounds are present; it is merely a measure of everything in the water besides H2O molecules that is small enough to pass through a 2‑micrometer filter. The higher the TDS reading, the higher the concentration of dissolved solids in the liquid. Some amount of TDS in water is normal, harmless, and sometimes healthy, depending on the specific solids present and the levels at which they occur.

Common Components of TDS

Dissolved solids in tap water are mostly inorganic salts, most commonly calcium, magnesium, potassium, sodium, chloride, sulfate, carbonate, and bicarbonates. Groundwater often also picks up nitrate, particularly in regions with heavy fertilizer use. Small amounts of natural organic matter, like tannins and humic and fulvic acids, round out the mixture. Given enough time, water dissolves these compounds on its journey from source to tap.

Sources of Dissolved Solids in Tap Water

Water will pick up different mixtures of soluble materials as it flows through different areas. Some of these compounds can originate from natural sources, such as plants, rock, soil, salt deposits, and saltwater intrusion in coastal areas. For example, as groundwater filters through soil and rocks, it picks up and absorbs minerals, like calcium, magnesium, and potassium.

Some types of TDS may also come from human activity. Common examples are chlorine from water treatment plants, lead from mining sites and old pipes and plumbing components, and pesticides and fertilizers in agricultural runoff.

Dissolved solids may also be deliberately introduced as mineral additives. Fluoride is a good example: some municipalities add the mineral to public water supplies to protect dental health. Over time, the water dissolves these contaminants and additives, thereby contributing to its TDS reading.

Why Should You Measure TDS in Your Drinking Water?

All the talk about TDS thus far, why does it matter for drinking water? The amount of dissolved solids in water can impact its quality, your health, pipes and appliances, and everyday tasks like cooking and cleaning. To better understand the role of TDS in drinking water, let’s delve deeper into its potential impacts.

Health and nutrition: Although high TDS isn’t inherently a health concern, it can sometimes indicate elevated levels of hazardous contaminants, like lead, copper, and arsenic. Conversely, moderate amounts of certain dissolved solids are necessary for proper body function. Beneficial minerals in water, such as magnesium and calcium, may help supplement people’s daily intake.

Learn more: The Health Risks of Lead | Effects of Arsenic in Drinking Water During Pregnancy

Flavor, odor, and appearance: Depending on the type and concentration of dissolved solids, high TDS tap water can impart a salty, bitter, metallic, or sulphuric taste, a very pronounced mouthfeel, an unpleasant smell, or a discolored or cloudy appearance. The higher the concentration of the offending compounds, the stronger the effect. On the flip side, some people describe water with extremely low TDS levels as tasting flat, insipid, flavorless, unrefreshing, or “dead.” According to a 2012 study, tasty, flavorful tap water requires a balance of magnesium, calcium, sulfate, and bicarbonate.

Learn more: Smelly Tap Water and How to Fix It | Why Does My Drinking Water Taste Like Metal?

Cleaning and showering: Water with excess dissolved calcium and magnesium can cause hard water deposits on various surfaces. As a result, you may notice spots and film on glass, dishes, and silverware out of the dishwasher, and stiff, dingy laundry. Soap scum may appear on sinks, tubs, and tiles, as well as on your skin and in your hair after showering.

Cooking: Cooking food or mixing beverages with elevated TDS water can alter the taste and texture. For instance, high levels of chlorine in water can impart a chemical-like taste in foods like rice, noodles, beans, and pasta, while coffee or tea may taste metallic. On the other hand, low TDS water typically pairs well with light foods and drinks by allowing their flavors to shine.

Learn more: Benefits of Cooking & Baking with Filtered Water | The Best Water for Making Coffee

Plumbing and household: Elevated levels (over 120 ppm) of certain TDS components, primarily calcium and magnesium, can cause hard water deposits to accumulate in pipes, plumbing, and water-using appliances. The scale buildup can narrow pipes, reduce water pressure, and corrode plumbing and fixtures. It may also force water heaters, boilers, and household appliances such as steam irons, dishwashers, and washing machines to work harder, shortening their lifespans, increasing energy use, and causing more frequent and potentially costly repairs.

Learn more: How Hard Water Damages Your Plumbing and Appliances

How to Measure Total Dissolved Solids in Tap Water

The simplest and most accessible way to measure TDS in drinking water is with a TDS meter, also known as a conductivity meter. This handheld meter generally works by passing an electric current between its two electrodes while submerged in the liquid. Because many dissolved solids carry an electric charge, the device measures the water’s electrical conductivity and estimates the TDS from that reading. Unfortunately, TDS meters usually don’t detect “uncharged” dissolved solids. That means toxic impurities like pharmaceuticals, PFAS, and chromium‑6 may go undetected, particularly at very low but harmful levels. TDS meters also don’t indicate the specific solids present or the levels at which they occur.

A DIY home water test kit or a professional laboratory water analysis is recommended to identify the types of TDS present and their levels. Also, municipalities are required to test public water supplies and issue annual water quality reports. So, if your water comes from the city, you can request the latest copy from your water provider, search for it on their website, or use the EPA’s CCR Finder Tool.

Learn more: 10 Common Problems a Water Test Can Detect in Tap Water | How to Read Your Water Quality Report

What is an Acceptable TDS Level in Tap Water?

There’s no enforceable limit for total dissolved solids in public drinking water sources in the United States. However, the Environmental Protection Agency (EPA) recommends that TDS concentrations should not exceed 500 mg/L or 500 ppm. The agency considers TDS an aesthetic issue rather than a health hazard and therefore classifies it as a secondary contaminant. But even with this recommendation, it is still important to test your water to determine which TDS are present and their concentrations. Total dissolved solids comprise a mix of hazardous and healthy elements, so you should always try to understand what your TDS readings comprise.

How to Reduce TDS in Tap Water

You have a few options for lowering TDS in your water supply. The ideal one for you will depend on the specific dissolved compounds in your water, which are usually determined by a water test.

Ion Exchange

Calcium and magnesium are primarily associated with hard water, so if concentrations are high (over 120 ppm), consider installing a water softener to prevent hard water issues in your home. Ion exchange softeners use electrically charged sodium or potassium ions to replace the dissolved hardness solids.

Water Distillation

Installing a water distiller is one of the few ways to achieve a near-zero TDS reading, if that’s your goal. Distillation involves turning water into steam, then collecting the steam in a separate container where it condenses back into water. Most of the dissolved solids get left behind because they can’t turn into vapor.

Reverse Osmosis

A reverse osmosis system will strip most types of TDS from water. Reverse osmosis works by forcing water through a semi-permeable membrane with pores so fine that only water molecules pass through. Together with pre- and post-filters, the membrane removes a broad range of dissolved solids, including arsenic, fluoride, bacteria, viruses, lead, mercury, chlorine, and pharmaceuticals.

Learn more: How Reverse Osmosis Works

Final Thoughts

Beyond H2O molecules, tap water may contain a mix of dissolved organic and inorganic compounds; some harmful and some beneficial. The presence (or lack) of some of these compounds can influence the water’s aesthetics, mineral profile, and safety. By measuring the TDS level, you can determine the total concentration of these dissolved compounds in your drinking water. However, since TDS doesn’t indicate the specific contaminants present or their levels, you shouldn’t use it alone to judge your water quality. Instead, have your water tested, then select a suitable treatment solution based on the test results.

If you need help choosing the best method to reduce TDS in your water, call SpringWell at 800-589-5592 or schedule a free water consultation. Our water experts will walk you through your options so you can make a confident, informed decision for your home.