What is TDS in Water? Total Dissolved Solids Explained

Water has a unique chemical and physical composition, and it’s this unique composition that allows water to bond, trap, and suspend/dissolve almost any substance. 

This is why many scientists commonly call water a universal solvent.

What is Total Dissolved Solids (TDS) in Water?

What is TDS? Total dissolved solids or, TDS for short, is a water quality parameter that measures the total concentration of inorganic material, natural particles, metals, chemicals, substances, compounds, salts and organic matter in water

Most commonly in water, total dissolved solids are made up of inorganic salts and organic compounds such as calcium, magnesium, potassium, sodium, heavy metals, carbonates, nitrates, chlorides, and sulfates.   

The measurement and regulation of TDS in drinking water was determined when the EPA established the National Secondary Drinking Water Regulations or NSDWRs for short. The NSDWRs are non-mandatory water quality standards that have been put in place for 15 different types of contaminants. 

The contaminants that are listed as NSDWRs have maximum contaminant levels that are not enforced and not considered to present any risk to human health

It is essential to know that TDS testing is done with a TDS test meter that measures the conductivity of water. This means that the total dissolved solids content of your drinking water, pre this testing, does not reflect uncharged contaminants such as bacteria, motor oil, gasoline, pharmaceuticals, pesticides, or PFAS. If you want to determine what contaminants are in your water, then you should purchase a water test or arrange for a professional laboratory test.

Common Total Dissolved Solids

In the list below, I’ve highlighted some of the common total dissolved solids, some harmful, some healthy, you’re likely to find in your drinking water:

  • Fluoride
  • Chloride
  • Calcium
  • Magnesium
  • Potassium
  • Aluminum
  • Iron
  • Copper
  • Zinc
  • Sulfates
  • Nitrates
  • Bicarbonates

Where Do Dissolved Solids in Water Come From?

Total dissolved solids may come from a number of different sources, with some substances occurring naturally in the environment and others being the result of human activity.

TDS sources from nature include substances such as minerals, salts and particles from organic compounds including groundwater, soil, lakes, springs, rocks, rivers, and plants. As an example, if water was to flow in natural underground springs, it would pick up minerals and microorganisms along the way from the surrounding rocks and plants, including potassium, magnesium and calcium compounds.

Human activity such as industrial agricultural processes can also result in greater amounts of TDS in household drinking water. For instance, agricultural runoff may leach pesticides into natural water sources. These particles typically aren’t fully filtered out during treatment before water is sent to our homes. Similar to agricultural runoff, industrial wastewater may also leach low concentrations of harmful particles, such as heavy metals, into water as urban runoff. This is especially common if you live in an urban setting.

Old lead pipes, which are still used in plumbing today, may leach small amounts of lead into water, while chlorine, a chemical contaminant, is added to water to disinfect it. Road salts applied to road surfaces for de-icing may also leach into water. Fluoride is one of the few particles that’s intentionally added to water in some states – it’s thought to improve oral health, but it may be linked to a number of health concerns when ingested even in low concentrations.

agricultural runoff source of high tds in water

How is TDS Measured?

Total dissolved solids (TDS) is measured in milligrams per liter (mg/L). This is otherwise referred to as parts per million (PPM), but don’t let this confuse you – both measurements are exactly the same and are used interchangeably, so you don’t need to convert one to the other.

The secondary drinking water regulations, produced by the EPA, report that the maximum TDS levels in water should be 500 PPM. That’s the maximum level of TDS present that’s safe to drink. Anything higher than this is risky, and anything higher than 1000 PPM is an unsafe TDS level. If your TDS levels are higher than 2,000 PPM/ milligrams per liter, then a specific water treatment system designed for higher TDS should be installed to properly reduce or remove TDS from your water.

How do you measure total dissolved solids in water? Before you can consider water treatment, you’ll want to know exactly what total dissolved solids (TDS) is present in your water. The easiest way to do this is to use a TDS meter, which you can buy online. This meter can indicate what TDS level your water has, and whether it’s considered low, average, or high.

Keep in mind that a TDS meter won’t indicate exactly which suspended impurities are present in water supplies, so once you know your TDS level, you might want to use an at-home water test kit or pay for a laboratory to test your water, so you know exactly what you’re dealing with. Your local authority is also legally required to test water routinely and produce an annual water quality report for your area, and can provide this to anyone who requests to see it.

what is tds

What Does High TDS in Water Mean?

One of the biggest concerns with high TDS water (excluding pH), is actually not the amount of total dissolved solids, it’s the concentration of calcium and magnesium mineral ions. 

These two minerals are responsible for making water hard, which can form scale in both plumbing and appliances. 

Scale from mineral deposits can cause damage and lead to some expensive repairs over time. If you have high TDS levels in your water and do not have a water softener, you will want to test the hardness of your water. 

The TDS of a water supply is mainly aesthetic. Water with lower TDS often tastes flat, while water with high TDS often has a slightly salty/ sodium or bitter taste and can be corrosive. By adjusting the amount of TDS in your water, you can achieve the desired taste.

👉 Read about the difference between hard water and soft water

What Are the Risks Associated With high TDS?

Of course, aside from the hard water issues linked with high TDS levels, there are also risks associated with human consumption of certain total dissolved solids present in water.

Generally, having elevated TDS levels isn’t an immediate sign of danger – chances are, it’ll just affect the taste of your water. With that said, if your total dissolved solid measurement comes to above 500, it’s worth investigating further into which suspended impurities in your water. If harmful impurities such as toxic metals and chemicals are making up a large portion of your TDS count, you may be harming your health by drinking water that’s laced with these contaminants.

If your TDS levels are above 1,000, you’re even more at risk – but again, it depends on the type of contaminants you’re dealing with. If your water contains a high level of particularly harmful impurities, you’re in more trouble when it comes to your health. You can use a testing kit or laboratory tests to determine whether your water contains any substances that could cause serious harm.

What Are the Acceptable Drinking Water TDS levels?

I’ve already mentioned that the maximum level of total dissolved solids (TDS) in water is 500 PPM or MG/ L – but what about the acceptable TDS level? Generally speaking, the amount of total dissolved solids that you want in your drinking water is up to you. Different people prefer different levels of TDS in their drinking water, just like how some people prefer mineral water over distilled water. 

That being said, most people agree that water with a TDS level of over 1,000 mg l/ppm is undrinkable. In 2003 the World Health Organization conducted a study to find out which TDS levels people prefer the most. 0 to 300 mg l/ppm of dissolved solids is the range that most people find to taste the best.

TDS in water

How to Measure TDS

Measuring water’s electrical conductivity – which is a determiner for how many chemicals, organic substances, compounds, salts and other particles are present – TDS using a TDS meter is easy. It’s best to measure the amount of dissolved ions in stagnant, not flowing, water, in your analysis, so start by filling a glass with water from your faucet.

Next, switch your TDS meter on and place it into the glass of water. A digital reading will automatically appear on the screen. Some TDS meters require you press a second button to keep the reading in place when you remove it from the water. If yours doesn’t have this option, simply note down the reading before you remove the meter.

Compare your reading to the table above to determine whether you have low TDS, acceptable TDS, elevated TDS or high TDS. A low TDS measurement is typically a good sign, but it can still be helpful to know which dissolved ions your water contains from here.

After conducting tests on your water and implementing a water filtration treatment, you can then measure your TDS again. You can take the water straight from your faucet, or, if you’ve used a separate unit to filter a batch of water, you can take your water from there. You should now have a low TDS water reading if your filtration treatment has proved effective.

Why is measuring TDS Level Important?

The levels of TDS in your water supply relate to water quality. Even if your drinking water contains total dissolved solids (such as minerals & salts) that won’t necessarily harm your health, they may still cause issues in water supplies.

Here are just a few reasons why you should consider using a TDS meter to find out the TDS reading of your water supply:

1. TDS Can Affect Your Health

Not all total dissolved solids in the water are harmful, but impurities such as pesticides and herbicides, lead, and bacteria pose a serious health risk. Human consumption of some chemicals and impurities, such as chlorine, fluoride and sulfur, are fine if they’re only found in low levels, but may be dangerous in larger quantities.

2. TDS Can Affect Water Taste and Smell

If your water has a metallic, bitter, chemical or rotten egg taste or odor, it’s likely you will have higher levels of TDS. Common aesthetic particles that can affect water taste and odor are chlorine, lead, arsenic, iron and sulfur. On the other hand, water sources that contain a high level of calcium and magnesium minerals may have a more pleasant alkaline taste.

3. TDS Can Alert You to Filter Maintenance Requirements

It’s not always easy to tell when your water treatment filter needs replacing. The filter may seem as if it’s performing well when it’s actually failing to trap impurities dissolved in water that travels into your home. Traditionally your taste buds can tell the difference, in this case, you can test the TDS in your water to make sure your filter is doing its job well and know exactly when you need to replace it with a new one.

4. TDS Can Damage Your Plumbing and Appliances

Hard water minerals such as calcium and magnesium, two common total dissolved solids, can produce scale in your pipes and plumbing. This can slow down water flow in your pipes and damage them over time. Calcium and magnesium can also damage water-based appliances and shorten their lifespans. Additional corrosive TDS such as iron can also damage your plumbing and appliances.

Related: Do I Need a Water Softener? 8 Telltale Signs

5. TDS Can Affect Your Cooking and Cleaning

If you cook with water containing certain total dissolved solids, it may affect the taste of your food. Chlorine, one of the common chemicals present in city water, for instance, may cause your food to take on an unpleasant taste when boiling. Hard water deposits and iron stains can also make your cleaning tasks around the house more difficult.

How to Reduce TDS in My Water?

Reverse Osmosis

Reverse osmosis has a TDS rejection rate of 92-98 percent, it is a great option for lowering the TDS levels of your drinking water. This drinking water filtration solution sends water through several filters and an RO membrane, which consists of tiny pores that only allow pure water particles to pass through, greatly reducing total dissolved solids in the product water. Total dissolved solids that are contained through the process are flushed down the drain along with some wastewater.

The TDS that are left over after the water has gone through the RO membrane usually depends on the level of TDS in the water source. Usually, RO can remove toxic metals and semi-metals such as copper, nitrate, lead and arsenic, chemicals such as chlorides, salt molecules, magnesium and calcium carbonate, microorganisms such as bacteria, and more.

RO systems are ideal for treating drinking water or whole-home water sources, as this type of water filtration system can be installed underneath your kitchen sink or at your home’s point of entry. These systems are effective in treating high levels of TDS in the water, but excessive magnesium and calcium minerals may damage the RO membrane.

Related: How Does a Reverse Osmosis System Work?

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Distillation is the oldest treatment for purifying water. During this process, heat is applied to water, causing it to boil until it becomes a gas and evaporates. This gas is usually collected in a cold and sterile container, where it can condense back into its liquid form.

It is because water has a boiling point that is usually lower than most suspended impurities (including minerals that make up TDS), the TDS are left behind when the water evaporates. The few TDS that succeed in evaporating and condensing with water are trapped in a small carbon filter in the distiller’s spout.

You don’t need to install a distiller at your water line; it’s a portable filtration option that can be set up on your kitchen countertop, near to an electric outlet, within minutes. The downside to this is that you don’t get on-demand access to water as you would with a whole-home or under-sink filter. Instead, you’ll produce batches of water, and the distillation process for each 1 gallon batch typically takes around 3-6 hours.

Distillation, like RO, can remove everything from calcium carbonate and magnesium to chloride molecules, salt, nitrate, lead, and other undesirable dissolved solids.

Related: Purified vs Distilled Water

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Deionization is based on ion-exchange principles. During this process, water flows through resin beds or resin beads depending on the system being used. 

The cation resin is what is used to exchange hydrogen in water for other positively charged ions, while the anion is the resin that is used to exchange hydroxide in water for other negatively charged ions. 

This process can be broken down further and you can separate the resin types into two beds or tanks, one for the Anions and one for the Cations. However, the most effective method is to combine both types of resin into one tank or bed.

The Best Option

RO + Deionization, with step down filtering most of the TDS can typically be removed via pre-filter methods, including sediment filters, carbon filters, then reverse osmosis (RO) membrane ( A Reverse Osmosis System). After the water goes through the reverse osmosis system, the water is sent through a DI system. By using a RO ahead of a DI system you can greatly increase the lifespan of the DI resin. This cuts overall DI costs significantly. The combination of RO and DI resins can remove nearly all impurities and reduce TDS levels to zero, resulting in pure water. Note that removing all the inorganic and organic substances, including minerals, may leave water tasting quite flat.

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