What is TDS in Water? Total Dissolved Solids Explained

What is TDS in Water

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 TDS in Water?

Total dissolved solids or, TDS for short, is a water quality parameter that measures the total concentration of charged organic and inorganic material in water

Most commonly the dissolved solids found in water are made up of inorganic salts such as calcium, magnesium, potassium, sodium, carbonates, nitrates, bicarbonates, chlorides, and sulfates.   

The measurement and regulation of TDS in 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 meter that measures the conductivity of water. This means that the TDS of your water does not reflect uncharged contaminants such as bacteria, motor oil, gasoline, pharmaceuticals, pesticides, or PFAS. If you want to know what contaminants are in your water, then you should purchase a water test.

What Does High TDS in Water Mean?

The biggest concern with high TDS in a water supply (excluding pH), is actually not the amount of total dissolved solids, it’s the concentration of calcium and magnesium. 

These two minerals are responsible for making water hard, which leads to scale build-up in both plumbing and appliances. 

This can lead to some expensive repairs over time. If you have high TDS in your water and do not have a water softener you will want to test the hardness of your water. 

The TDS of water is mainly aesthetic, water with lower TDS tends to taste flat, while water with high TDS tends to have a slightly salty taste. 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 is the Acceptable TDS in Drinking Water?

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 1,200 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 Remove TDS From Drinking Water?

Distillation

Distillation is the oldest method for purifying water. During this process, heat is applied to water 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 contaminants (including minerals that make up TDS), the TDS are left behind when the water evaporates.

Reverse Osmosis

Reverse osmosis has a TDS rejection rate of 92-97 percent, it is a great option for lowering the TDS levels of your drinking water. The TDS that is left over after the water has gone through the RO membrane usually depends on the level of TDS in the water source.

Deionization

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 reverse osmosis and DI resins can remove nearly all contaminants and reduce TDS levels to zero.