In Brief: What is TDS in Water?
TDS is a measure of the number of impurities present in water. It is made up of organic matter, inorganic matter, and ions. Water with high levels of TDS is not dangerous to drink but it can have many disadvantages. An absence of TDS in water also has its drawbacks. TDS can be measured and controlled to make it an ideal amount.
TDS in water is a common phenomenon across the globe. Most homes are supplied with water from natural or man-made sources.
In both cases, the water passes through many channels before it reaches the faucets in a house. This is how TDS collects in it as water is a universal solvent.
What is TDS in Water?
TDS stands for Total Dissolved Solids and is a measure for the number of contaminants present in water.[1]
These contaminants are larger than 2 microns in size and can be easily filtered out with a fine sieve.
TDS usually consists of both organic and inorganic materials including minerals and ions. Organic matter may include bacteria, viruses, plankton, or other microorganisms.
Some of the inorganic matter are calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates. Primarily, there is more inorganic content.
The contaminants are typically in ionized, molecular, or micro-granular (colloidal sol) suspended form.
These compounds get dissolved into the water through a variety of sources. Before water reaches you through your faucet, it passes through many different surfaces.
These could be pipes, wells, or channels. Some of these surfaces are made of stone, metals, plastics, and other natural or man-made materials.
With prolonged contact with such surfaces, a lot of particles get dissolved into the water through its motion.
Sometimes, water is even exposed to minerals, salts, and chemicals because of fertilizers, water treatment, or run-off from the roads.
It may even get exposed to sewage, industrial wastewater, or natural sources like deposits, springs, and seawater.
As a result of all these processes, there could be many different contaminants in water that compromise its purity. The TDS level of a water supply indicates how many such contaminants are present.
All the contents of TDS are either positively charged ions (cations) or negatively charged ions (anions).
Their total sum gives us a quantitative measure of the quality of water. The TDS test cannot however describe other information about water quality like hardness, corrosion, or taste.
The TDS measure only describes the types of ions present in water and not the nature of these ions.
Nevertheless, it provides a general idea about the aesthetic characteristics of potable water. It also gives an aggregate of the presence of chemical contaminants.
What are Acceptable Levels of TDS in Drinking Water and How to Measure?
There are two principal methods of measuring TDS levels: gravimetric analysis and conductivity. These laboratory techniques are used for measuring TDS in water bodies.
When measuring TDS levels at home, it is generally to assess the quality of drinking water. There are various tools you can use to check TDS levels for drinking water at home.
These tools use the same principle methods to provide information about the quality of the potable water.
Acceptable Levels of TDS in Drinking Water
Generally, a TDS level of more than 50 milligrams per liter and less than 900 milligrams per liter is suitable for drinking water.
Indian Bureau of Standards has 500 pmm as the max limit of healthy drinking water. [2] But the limit set by WHO is lower, at 300 ppm. [3]
The following table gives a measure of acceptable levels of TDS in drinking water.
| TDS Level (Milligram/Litre) Drinking | Water Quality |
|---|---|
| Less than 50 | Not good as it lacks essential minerals |
| 50 - 150 | Excellent |
| 150 - 350 | Good |
| 350 - 500 | Fairly acceptable |
| 500 - 900 | Borderline acceptable |
| 900 - 1200 | Not good for health |
| more than 1200 | Unacceptable |
How to Measure TDS?
To measure the level of TDS in your water, you will need a TDS meter. There is a wide variety of instruments that can be used to measure TDS levels.
Some of these include portable meters, benchtop meters, colorimeters, single parameter sensors, multiparameter sondes & CTD, and online meters.
Once you have chosen a measuring instrument, you will need to take two readings. First, submerge the tester’s probes in a glass of tap water to measure the TDS of the raw feed water.
Then, fill a glass with purified water from the faucet of your RO system and submerge the probes. Next, subtract the RO TDS from the Tap TDS and multiply the result with 100. Then, divide this product by the Tap TDS.
The calculated value is the rejection percentage that indicates the number of TDS removed by the RO system. Knowing the Tap TDS, RO TDS, and rejection percentage will inform you about the required changes for the ideal TDS level.
If your RO system or its filter is new, don’t use the first tank of water to test. This may alter the TDS readings due to sanitizer or carbon fines.
Benefits of TDS in Water
Though TDS may consist of compounds that make water impure, there are certain benefits to having TDS in drinking water. Water lacking in TDS is corrosive in nature.
This is particularly bad for metals in pipes as the absence of TDS may cause leaching. Water containing an optimal level of TDS is also better in taste. The lack of TDS leaves water tasting rather flat.
As a large portion of TDS comprises minerals like calcium and magnesium, they affect the pH of the water. An optimized pH in water is believed to improve the drinking experience and augment good health.
TDS in water also makes it ideal for plant cultivation in practices like hydroponics and aquaculture. But it must be noted that these benefits only apply when the TDS level is above 50 PPM and below 900 PPM.
Problems with High TDS in Water
TDS levels higher than 900 milligrams per liter make water unfit for consumption.
In fact, a level above 350 milligrams per liter is also not considered ideal.
Though these levels aren’t harmful to one’s health, they do have some disadvantages.
High levels of TDS compromise the taste of drinking water. Water may taste acidic, salty, or brackish depending on the amount of TDS.
Water with high TDS is safe to drink but there are chances of it containing hazardous substances like lead or copper. These can be very dangerous for little children whose immune systems are still developing.
Other than consumption factors, high TDS can cause different problems in a home. These impurities shorten the lives of water filters and increase the amount of maintenance required.
If used in cooking, water with high TDS levels can change the flavor of food.
High TDS also makes it harder to wash up or clean, increasing the amount of soap, water, and time needed.
How TDS can be Controlled?
There are multiple ways to control TDS levels in your water supply. Which method is best depends on the type and nature of the contaminants.
Reverse Osmosis (RO)
This is a method that removes TDS by pushing water through a synthetic membrane.
The RO membrane has very minute pores that only allow molecules smaller than 0.0001 microns to pass. This is enough to sufficiently reduce the amount of TDS in water.
Distillation
In this technique, water is boiled to the point of evaporation. The water vapors are then passed to a different cool surface.
The vapors condense to give purified water without any of the salts as they were unable to vaporize. This is a very effective technique but more suitable for laboratories than households.
Deionization
A relatively more recent solution for homes, deionization uses electrodes to remove cations in water.
This system passes the water through a positive and negative electrode to separate the positive ions.
The remaining content is deionized water with high purity. However, this water needs additional filtering to remove non-ionic impurities.
To select a suitable method, you may conduct some advanced tests by sending a water sample to a certified lab. In general, reverse osmosis is the most popular solution to control TDS.
Summary
TDS, or total dissolved solids, is exactly what the name indicates. It is the sum of the solids dissolved in water, which usually involves charged ions. TDS comprises both organic and inorganic materials and its composition varies across water sources.
There is an ideal amount of TDS that affects the water’s potability and aesthetics. Levels of TDS below or above that ideal amount can compromise the drinking experience.
Though water with high levels of TDS isn’t dangerous for adult consumption, it has various disadvantages. The amount of TDS present in water can be measured using a variety of tools.
The ideal amount of TDS in water ranges from 50 PPM to 350 PPM. One can control the amount of TDS in their drinking water by any of the three processes. These are reverse osmosis, distillation, and deionization.