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What is TDS (Total Dissolved Solids) in Drinking Water?

truth about tds in waterTotal Dissolved Solids or TDS is the term used to describe the amounts of inorganic salts and organic matter present in solution in drinking water. The main compounds described as dissolved solids are magnesium, calcium, potassium, sodium cations and carbonate, chloride, nitrate anions, hydro carbonate, and sulfate. TDS level refers to how much total dissolved solids are present in the drinking water.

What are the Sources of Total Dissolved Solids?

The sources of dissolved solids in drinking water are different and numerous. These can be either due to natural or human activities. For example, the TDS level is high if the water flows through a region where rocks have a high salt content. De-icing roads with salt might also increase the TDS level in the water as the salt used might end up in water sources.

Some of the most important sources of TDS are:

  • Natural environmental features (carbonate deposits, mineral springs, salt deposits, seawater intrusions)
  • Drinking water chemical treatment
  • Wastewater discharges
  • Anti-skid materials
  • Salts used for road de-icing
  • Agricultural runoff
  • Stormwater

Why Should You Measure Total Dissolved Solids?

The total dissolved solids should be measured because the TDS level is an indicator that provides insights into general drinking water quality. TDS levels may vary due to human, agricultural, or industrial activities. For example, higher TDS levels are a direct consequence of pollution. Heavy metals, pesticides, or other toxic ions are released every day, thus contaminating different drinking water sources. 

Although high levels of calcium, magnesium, and other useful minerals are desired, the situation changes when the anions and cations result from human activities such as gardens’ fertilizing, wastewater discharges, road de-icing, and other human activities. Lead and copper pose a health hazard, being responsible for nervous system damage or nausea. High levels of heavy metals require constant monitoring.

Also, even if calcium and magnesium do not have harmful effects on human health, they cause water hardness, staining, or scale formation. Drinking water tends to have a salty, bitter taste and an unpleasant odor. Chlorine high levels tend to change the taste of cooked food.

Monitoring the TDS level is important for filters, plumbing, and appliances maintenance. High levels of salts build up on plumbing and involve high costs related to pipe and appliances replacements. Knowing the types of dissolved solids and their concentration is essential when watering vegetables. High TDS levels of potassium and nitrates are beneficial for plants. However, toxic compounds might be absorbed by the plants.

How is TDS measured?

tds measurement in drinking waterTotal Dissolved Solids level is measured on a quantity scale, either in parts per million (PPM) or in mg/L. There are two methods used for measuring TDS: conductivity and gravimetric.

Commonly used and considered the most accurate method for measuring TDS levels is gravimetric measurement. The gravimetric method involves evaporating a water sample and weighing the remains with an analytical balance. Despite its effectiveness, this is an expensive method that is only used in chemical labs.

Drinking water can be tested by everyone using TDS meters, devices that use the electrical conductivity of water. These digital or analog indicators estimate the TDS level. Using a TDS meter is easy. The only materials needed to measure the TDS level are a glass of water (the sample) and the meter. After the indicator is put in the water, it will indicate the TDS level.  

It is important to notice that these devices do not show what minerals are present in the water. For a better analysis of the drinking water, it is recommended to perform a lab test and purchase an effective water filtration system.

What is the TDS Calculation Formula?

The TDS calculation formula when using the conductivity method is TDS = KE x EC

TDS is measured in mg/L. KE represents the correlation factor that depends on the liquid used as a sample, and it varies according to the atmospheric conditions. EC is the conductivity of the sample, and it is obtained using an electrical conductivity meter.

If the evaporation method is used, the TDS calculation formula is different:TDS = [(A-B)] x 100] mL sample

A stands for the weight of the evaporating dish + the filtrate and B stands for the weight of the empty evaporating dish. A scale capable of weighing in mg is needed to use this method, which might not always be available.

TDS Level Chart for Drinking Water

The TDS level is a good indicator of water purity, and it shows if the drinking water is fit for consumption. This level is measured in parts per million (PPM).

TDS in Water (PPM)

Suitability for drinking water

50 – 150 PPM

Excellent for drinking

150 – 250 PPM


250 – 300 PPM


300 – 500 PPM

Poor, not fit for consumption

Above 1200 PPM


What is the Best TDS Level for Drinking Water?

According to the World Health Organisation (WHO), the best TDS level for drinking water is less than 300 PPM. Any values higher than 300 PPM are found in water with a salty taste and a high concentration of minerals. This water will require a proper purification system that holds a fair amount of the dissolved solids.

Is High TDS Water Harmful?

High TDS levels in water are not necessarily harmful, but they are a good indicator of further investigations needed. Commonly, a high TDS level is caused by the presence of chlorides, potassium, and sodium. These ions have minor or short-term effects. However, toxic ions such as nitrates, cadmium, or arsenic may be dissolved in water. To make sure no heavy metals or other poisonous ions pollute the water, lab analyses are needed.

How to Reduce TDS in Water

tds methods to reduceHigh TDS levels might negatively affect human health (toxic ions), plumbing, and appliances. Potassium, sodium, magnesium, iron, and other minerals tend to build up on plumbing and other surfaces. They are also responsible for water hardness.

When municipal water has high TDS levels, it is recommended to find solutions for reducing these TDS. The water from other sources such as wells or springs also needs treatment before using for consumption or garden watering.

The most effective water treatment method for reducing or removing TDS is reverse osmosis. To better understand what water purification is through reverse osmosis, one must first know how it works. This method removes TDS by forcing water under pressure through a synthetic membrane that contains microscopic pores. Molecules smaller than 0.0001 microns can pass through. Thus the molecules of the dissolved solid (larger than water ones) remain trapped in the membrane.

Distillation is another method used to lower the TDS levels. This process involves boiling water to produce vapors that rise to a cool surface. Dissolved solids are unable to vaporize so will remain in the boiling solution.

Deionisation is an excellent solution for obtaining highly purified de-ionized water. Water flows through a positive and negative electrode. The ion-selective membranes force the positive ions from the water to move towards the negative electrode. This water treatment system is used in conjunction with a reverse osmosis system that removes the non-ionic organic compounds.

For the areas where the water contains high TDS levels and other contaminants, it is recommended to use water purifiers that combine reverse osmosis, UV, and TDS controllers.

Types of Total Dissolved Solids

There are numerous types of dissolved solids but the most common fall under four big TDS categories:

  • Minerals – Magnesium, potassium, sodium, calcium, bicarbonates, chlorides, and sulfates end up in water from natural sources such as mineral-rich rocks. These minerals improve the water taste and are beneficial for human health.
  • Salts – These compounds may naturally occur in groundwater, but human activities may also affect their levels.
  • Dissolved metals – Heavy metals commonly get into water through pollution. Human activities like mining or industrial waste may result in metals leaking into drinking water sources.
  • Organic matter – Dissolved organic matter is typically produced by the natural decomposition of plant material or algae. However, most of the organic matter is removed via the treatment of municipal water.

What are the Effects of TDS?

The most common effects of TDS are as follows: 

  • Effects on Human Life: High levels of TDS are not necessarily bad for health. Minerals like calcium, magnesium, sodium, and potassium have beneficial effects. However, a high TDS level might indicate the presence of toxic ions. Heavy metals, pesticides, or other compounds produce major health issues if not removed from drinking water.
  • Effects on Environment: Dissolved salts do not always have a positive effect on the environment. High levels of TDS but also lower levels might negatively affect aquatic life. Many aquatic plants will have limited growth while others simply die. Moreover, higher concentrations of dissolved solids may reduce water clarity, thus decreasing the photosynthesis process and increasing the water temperature.  Salts dehydrate the animals’ skin, so high concentrations of these compounds lead to animals’ death.
  • Effects on Technical Equipment: A high TDS level might indicate an elevated concentration of corrosive compounds in the water. Although these dissolved solids do not affect human health, they harm plumbing and different surfaces. High amounts of iron, chloride, copper, zinc, or manganese cause water corrosivity and cause technical damage. Pipes get clogged and rusty, while household fixtures get stains. Another unwanted effect of high levels of dissolved solids is scaling and sedimentation. Scale is the term used for mineral deposits that restrict water flow in different appliances such as boilers, heat exchangers, or pipes. Sedimentation, on the other hand, represents a loose deposit of non-mineral solids in plumbing systems. Lower levels of TDS also have undesired effects. A low TDS level is associated with a low pH and low alkalinity. Due to the low dissolved solids concentration and the lack of alkalinity, the water with TDS below 50 PPM exhibits corrosive tendencies. Plumbing systems and fixtures get attacked, and the best option, in this case, is the pH correction that increases the TDS level.

What is the Most Effective Water Filtration System for TDS?

The most effective water filtration system for TDS is reverse osmosis water treatment. Reverse osmosis systems are effective against heavy metals (iron, copper, lead), salts, magnesium, calcium, sulfates, arsenic, nitrates, phosphorus, or fluoride. High-end reverse osmosis systems can reduce up to 93% – 97% of TDS.

Another effective water filter type for TDS is activated carbon filters. Activated carbon filters are effective against pesticides, industrial solvents, disinfectants and their by-products, and many other harmful substances. However, these filters are unable to capture heavy metals, mineral ions, or microbes like reverse osmosis does. Suppose the exact water composition is known, and there are no toxic ions present. In that case, activated carbon filters do a great job of purifying water without removing valuable minerals such as calcium, potassium, or magnesium.

If the water composition is unknown and the TDS levels are high, a reverse osmosis water purifying system is a better choice. Not only will it reduce the high percentage of dissolved solids, but it will also remove harmful microorganisms such as microbes.

Other water filtration types cannot remove or reduce the TDS high levels in the water. However, they can be used in conjunction with a reverse osmosis system for better drinking water quality. 

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