Total Dissolved Solids, also known as TDS, are inorganic compounds found in water, such as salts, heavy metals, and some traces of organic compounds dissolved in water.

Excluding the organic matters that are sometimes naturally present in water and the environment, some of these compounds or substances can be essential in life. But, it can be harmful when taken more than the desired amount needed by the body.

The total dissolved solids present in water are among the leading causes of turbidity and sediments in drinking water. When left unfiltered, total dissolved solids can be the cause of various diseases.

Total dissolved solids (TDS) measure the combined total of organic and inorganic substances contained in a liquid. This includes anything present in water other than the pure H20 molecules. These solids are primarily minerals, salts, and organic matter that can be a general indicator of water quality.

What are Total Dissolved Solids in Water?

Water is called a universal solvent because it’s able to dissolve and absorb molecules from many different substances.

TDS is defined as the combined content of all inorganic and organic substances contained in a liquid that are present in a molecular, ionized or microgranular suspended form.

In other words, it’s all of the minerals, salts, and organic particles in the water that you can’t see.

Not all of these organic compounds are harmful, and many are naturally present in our environment. Some of these minerals include potassium, calcium, magnesium, chlorides, bicarbonates, and sulfates.

However, they can be harmful if you take in more than your body needs, or if heavy metals such as iron are present.

TDS in our water supplies can come from:

• natural water sources
• sewage
• urban run-off
• industrial wastewater
• chemicals during water treatment
• pipes and pipe fittings
• stormwater
• agricultural run-off
• road de-icing salts

The TDS in Drinking Water

The TDS in drinking water comes from natural water sources, sewage, urban run-off, industrial wastewater and chemicals used in the water treatment process, and the hardware or piping used to distribute water. Higher TDS was brought by natural environment features like salt deposits, mineral springs, seawater intrusion, and carbonate deposits in the US.

Other sources may include anti-skid materials, salts used for road de-icing, stormwater, agricultural runoff, water treatment chemicals, and point/non-point wastewater discharges.

In general, the total dissolved solids concentration is the total cations (positively charged) and anions (negatively charged) ions in the water.  Thus, the total dissolved solids test gives a qualitative measure of the number of dissolved ions but does not tell us nature or ion relationships.

In addition, the test does not provide us insight into the specific water quality issues, such as Elevated Hardness (mineral content in water), Salty Taste, or Corrosiveness (also called aggressive water, which is how water dissolves with other materials).

Therefore, the total dissolved solids test is used as an indicator test to determine the general quality of the water.  The sources of total dissolved solids can include all of the dissolved cations and anions. Still, the following table can be used to generalize the relationship of TDS to water quality problems.

TDS Meter

Many people are conscious of TDS meters. It measures the water’s electrical conductivity, which can be connected with the amount of TDS. Meanwhile, a TDS meter can’t directly measure heavy metal contaminants like arsenic and lead. It does not indicate whether or not the water filter works properly to decrease this type of contaminants.

The normal TDS level ranges from 50 ppm to 1,000 ppm. On the other hand, the National Sanitary Foundation (NSF) International does not certify the use of the TDS meters.

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

Total Dissolved Solids (TDS) are measured in milligrams per unit volume of water (mg/L) and are also referred to as parts per million (ppm). For drinking water, the maximum concentration level set by EPA is 500 mg/L.

Factors Affecting TDS

High Flow Rates

When we talk about the TSS concentrations, the flow rate of a body of water can be a major factor. Fast running water can have large-sized and more sediment. Heavy rains can pick up clay, sand, silt, and other particles like tire particles, leaves, and soil. Moreover, a change in the flow rate can affect total suspended solids. If the direction or the speed of the current water increase, the particulate substance from the bottom sediments may be suspended.

Soil Erosion

Soil erosion is due to the troubles on the surface of the land. It can be caused by illegal logging, forest fires, mining, and construction. The particles of eroded soil can be carried via the stormwater into the surface water. With this, it can increase the level of TDS and TSS in the water.

Urban Runoff

When the storm comes, the debris and solid particles from the commercial or residential areas can be washed away into the streams. Due to a large amount of pavement in cities, there is an increase in infiltration and increase in velocity. The natural settling areas are removed. Through the storm, the sediments are carried into rivers and creeks.

Overflow of the Septic and Wastewater System

The particles from the wastewater treatment plants can also contribute to the suspension of solids in the stream. The wastewater from residential areas contains human wastes, food residue, and other materials that we flush in the drains. Most of the solids are already eliminated from the water at the plant. However, not everything is eliminated during the treatment.

Rotting Animals and Plants

As animals and plants decay, there are suspended organic particles which can be released. This can all contribute to TDS and TSS concentration in the drinking water.

Bottom-Feeding Fish

Bottom-feeding fish like carp can disturb the sediments since they tend to remove vegetation. Indeed, these sediments can add to TDS and TSS.