Total Dissolved Solids or TDS is the total charged mineral content of water. Apart from minerals, it also comprises metals, anions, cations, and inorganic salts such as potassium, sodium, bicarbonates, chloride, and sulfates dissolved in the water. All these impurities are measured using a TDS tester.
A TDS tester gives a qualitative measure of the number of ions in the water but not the nature of relationships of ions. It doesn’t provide insight on the water quality issues in the water such as salty taste, corrosiveness or elevated hardness. Here is the generalized relationship of TDS to water-quality problems:
| Cations with Carbonates
CaCO3, MgCO3, etc. |
Associated with hardness, scale information, bitter taste |
| Cations with Chloride
NaCl, KCl, etc. |
Salty or brackish taste, increased corrosivity |
An increased quantity of TDS is not a health hazard. In fact, it is only a secondary drinking water standard that is regulated because it is more of an aesthetic than a health hazard. Increased TDS amount indicates:
TDS in drinking water originates from natural resources, urban runoffs, sewage, industrial wastewater and chemicals used in the water treatment process. The nature of the piping or hardware to convey the water in the water treatment facilities also contribute to the TDS in the water.
In the US, TDS come from mineral springs, salt deposits, carbonate deposits, seawater intrusion and other sources such as salts from road de-icing, anti-skid materials, drinking water treatment materials, agricultural runoffs, stormwater, point/non-point wastewater discharges.
Municipal water treatment facilities get water mostly in freshwater sources such as streams, rivers, lakes or in underground waters. The quality of the water of these water sources is full of various minerals, ions, and salts. these dissolved solids are a mix of harmful and unharmful chemicals. That is why when this water passes through water treatments these impurities or contaminants are removed. When the water reaches homes, it is already safe for drinking.
Pre-Sedimentation is an area where treatment process starts. The raw water from the water source is delivered to the headworks of water treatment plant to undergo the five major unit water treatment processes. The five major unit processes are discussed subsequently. These processes make water safe to drink.
Chemicals used in this process breaks down naturally occurring organic matter such as decaying leaves and other plant material. One common chemical coagulant used is aluminum sulfate, a primary coagulant. A polymer or organic compounds are added to the water to strengthen primary coagulant bonding chains.
The coagulants are added to the rapid mix unit where turbulent mixing takes place in order to disperse the raw water into the coagulation process. The coagulants create a compression of fine particles into large ones which will then be removed later on through skimming, draining and filtering.
Coagulated water passes through the flocculation process. This process is a slow stirring movement that moves the small particles to form a floc. Here, floc particles and the sediments in the water meet. The meeting between floc and sediments is due to the hydraulic or mechanical mixing. The mixed up of flox and sediments form on the surface of the water, then it will be easier remove them by sedimentation and filtration.
Sedimentation is the removal of suspended solids (particles) that are heavier than the water. The reason behind this is to lessen the particulate load on the filters for the next process. Sedimentation is done by lowering the velocity of the water being treated below the point where it can transport the suspended material. This allows gravitational forces to remove particles that are suspended.
When water becomes still, sediments move toward the bottom of the basin. This process removes 90% of the solids in the water. The clear water on the surface is transported to the filter gallery to get rid of the remaining 10% of the solids.
This time, the water passes from pre-sedimentation building to the filtration facility. But before going to the filtration facility, chlorine is added to start the disinfection process. Disinfection process kills or inactivates most microorganisms present in the water such as bacteria, viruses or parasitic protozoans. Pathogenic organisms are the microscopic “bugs” in the water. They bring waterborne diseases such as giardiasis, typhoid, dysentery, cholera, and gastroenteritis.
After disinfection with chlorine, the water goes through the filtration facility to be filtered that last up to most of the time of the whole water treatment process. Filtration process lets the water pass through a filter material made out of bed of coal, sand or other granular substance to remove any remaining particles not removed during the sedimentation process.
The materials of the filter work like a superb strainer of the remaining particulates. Water treatment plant uses rapid rate multimedia gravity filter beds. When these filters become full of particles, they “backwash”, a procedure that lets the water run backward to release the trapped particles collected in the drain troughs.
The water that is collected from the bottom of the filters is now considered potable. But before it leaves the water treatment plant, a second round of chlorine is added to the water to provide assurance and to serve as the post-disinfection. In addition to chlorine, fluoride is also added. The fluoride in the water helps strengthen the teeth while also preventing decay.
The United States Public Health Service has determined the optimum concentration for fluoride in United States water to be in the range of 0.7 to 1.2 parts per million. e water treatment plants enough fluoride to raise that level to .9 parts per million. The fluoride level is measured daily at the water treatment plant and monthly at the tap to make sure it is sufficient to meet the concentration recommended by USPHS.
TDS is expressed in units of mg per unit volume of water (mg/l) or also referred to as parts per million (ppm). A natural mineral water has a TDS value of 100-200 mg/l. The tap water would also have the same levels of TDS but in areas with a high concentration level of minerals, natural tap water would also be high.
Water filtering technologies such as reverse osmosis, ion exchange, and distillation can reduce TDS level close to zero but active carbon filters can’t filter out TDS. World Health Organization (WHO) asked a panel of testers and came to the following conclusions on the preferable level of TDS in water (mg/l):
Above 1,200 – Unacceptable
1,200-900 – Poor
900-600 – Fair
600-300 – Good
300-less – Excellent
For most distilled mineral water, it has higher TDs which can be just good enough for tap waters. WHO and other institutions that regulate water quality consider values up to 500 mg/l to be safe and 2,000 mg/l is safe for temporary consumption if there’s no available water.
Below 500 mg/l has no scientific evidence that it could have any difference and 2,000 mg/l below has no negative health impact. However, there were no findings to show higher levels of calcium in water have a health impact. TDS level, in this case, is not sufficient to conclude negative impact because TDS meter does not specify different parameters that constitute the final number.
It is also worth noting that higher TDS parameter gives a heavier taste in the water.
A TDS tester shows the number of dissolved solids in the water. The higher the number the more impurities. Water filter companies use this as an argument that you can use TDS tester to reduce that level in your water. They also include the fact that TDS tester is a hassle-free and inexpensive device you have to monitor the TDS in your home water.
On the other hand, real tests measure all possible contaminants in the water. These contaminants are important determinants of the water quality so that they can be subject to sophisticated and expensive labs. Water quality testing is still important yet using a TDS tester might not give you the right information you need.
However, if you do have high TDS content in your water and choose to use a water treatment system, make sure to maintain the system that is according to the instruction of the manufacturer. This includes changing filters regularly.
Jennifer Moran is the author and the social media manager at The Berkey. She has been working and passionate about writing for over four years. When she isn’t glued to a laptop screen, she spends time playing tennis, practicing yoga, and trying very hard not to sleep in the meditation. You can reach her at jennifer (at) the berkey (dot) com.
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