TDS: A Key Indicator of Water Quality

TDS (Total Dissolved Solids) is one of the most important indicators for measuring water quality. It represents the total amount of dissolved solids in water, including inorganic salts (such as calcium, magnesium, sodium, potassium) and a small quantity of organic matter. These substances enter the water through natural processes or human activities, directly affecting the taste, health, and applications of the water.

Sources of TDS

Natural sources
- Groundwater dissolves minerals such as calcium, magnesium, iron, and silicates during contact with soil and rocks.
- Natural sediments in rivers and lakes dissolve to form inorganic salts.
Human activities
- Agriculture: Fertilizers and pesticides infiltrate into water bodies, increasing nitrate and phosphate content.
- Industry: Discharge of heavy metals and chemicals in industrial wastewater.
- Urban sewage: Sodium ions, chloride ions, etc., in domestic sewage.
Water treatment process
- Chlorination disinfection and softening treatment may increase the concentration of certain ions.

Types of TDS

Calcium
Potassium
Arsenic
Chlorine
Copper
Magnesium
Zinc
Iron
Sodium
Lead
Aluminum
Chloride
Fluoride
Sulfate
Bicarbonate
Pesticides

TDS Range

Table 1: TDS Range and Its Corresponding Water Quality
TDS	Water Quality
< 50–250 ppm	Low: Lacking minerals such as calcium, magnesium, and zinc.
300–500 ppm	Ideal: This level is the optimal point for TDS in drinking water. The water most likely contains minerals and do not taste flat.
600–900 ppm	Not great: Consider using a reverse osmosis system to filter TDS.
1000–2000 ppm	Bad: It is not recommended to drink water at this TDS level.
> 2000 ppm	Unacceptable: A TDS level above 2000 ppm is unsafe, and household filters cannot properly filter this level of contamination.

TDS Standards for Drinking Water in Various Countries

World Health Organization (WHO): Recommends drinking water TDS ≤ 500 ppm.
China National Standard (GB 5749-2022): Drinking water TDS ≤ 1000 ppm.
U.S. EPA Standard: Drinking water TDS ≤ 500 ppm.

How to Measure TDS?

Using a TDS meter is the simplest way to measure TDS. For example, if the TDS meter shows 100 ppm, it means that out of 1 million particles, 100 are dissolved ions. This would be considered a low TDS level.

However, the TDS meter cannot accurately identify the type of TDS, so it is recommended to use it in conjunction with a home water quality test kit or laboratory water quality analyzer.

Two TDS meters, one white TDS meter inserted into water measuring TDS

How to Reduce TDS?

Certain water treatment systems are effective methods to reduce or remove TDS from water, especially if the TDS level is 500 ppm or higher. There are many useful filtration systems depending on the type of TDS your water contains, but reverse osmosis systems, water distillers, and deionization are comprehensive systems that can reduce a majority of total dissolved solids.

Reverse Osmosis
A reverse osmosis system is one of the most comprehensive filters to remove contaminants. It uses pressure to push unfiltered water through semipermeable membrane. The membrane has small pores that block contaminants, such as total dissolved solids, but allow clean water to flow through to the other side.
Water Distillation
Distillation is a water treatment method that mimics how water is purified in nature – through evaporation in the atmosphere. Water distillers convert water into steam, eliminating total dissolved solids and other contaminants because they cannot furn into steam as water can. Once the water returns to its liquid form, it is contaminant free.
Deionization
Deionization systems remove total dissolved solids through ion exchange, using resins that control the electrical charge of ions. Water ions replace charged ions from total dissolved solids. The water produced is highly pure, so deionization cartridges are often referred to as high purity filters.

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