One of the simplest and easiest ways to gauge your water quality is to measure its TDS, or Total Dissolved Solids. Actually it is so easy and cheap to buy a TDS meter that a lot of people unintentionally link TDS with water contamination in a simple way. But is it really appropriate and what is TDS exactly?
What is TDS and what is included in TDS？
Total dissolved solids (TDS) is a measure of the combined content of mostly inorganic and some organic substances present in a liquid in ionized, molecular, or other dissolved form. The principal constituents are usually calcium, magnesium, sodium, and potassium cations and carbonate, hydrogencarbonate, chloride, sulfate, and nitrate anions. Dissolved organic matters can also present in TDS. TDS is measured in parts per million (ppm), which is equivalent to milligram in liter of water.
The following list details some common total dissolved solids that may be present in your water.
- Calcium
- Chloride
- Magnesium
- Sodium
- Potassium
- Zinc
- Aluminum
- Copper
- Lead
- Arsenic
- Iron
- Chlorine
- Sodium
- Fluoride
- Bicarbonates
- Sulfates
- Pesticides
- Herbicides
Sources of TDS in water
Total dissolved solids can come from all manner of sources. Water is a good solvent in leaching things it encounters. Natural materials may leach into water from soils and rocks as water runs through. Human activities also contribute to TDS, from industrial and agricultural runoff to things like deicing. Even the pipes and plumbing materials used to carry water to a home may be a TDS source.
Health effects of TDS in drinking water
Depending on what is in the TDS of your water, TDS is not necessarily a health hazard. Minerals like calcium and magnesium at lower level can be helpful for human body, even though the water may not taste that good. On the other hand, any level of pesticides can be harmful. TDS is not an EPA regulated contamination indicator. Yet high TDS is usually undesirable, and may have potential health effects. EPA recommends treatment when TDS concentrations exceed 500 ppm. And readings above 1000 ppm are considered unsafe for human consumption. Again, it is important to remember that when it comes to your health, the type of dissolved solids in your water is more important than the amount.
What water treatment technology reduces TDS
TDS in water is totally dissolved, only certain water treatment technology can reduce TDS.
Reverse osmosis
A reverse osmosis system uses multiple filtration stages and a semi-permeable membrane to reduce more than 95% of TDS. This type of treatment system is common water treatment plants and wastewater treatment plants. That said, it can also be installed underneath a kitchen sink or a home’s point of entry. One can also find countertop reverse osmosis filters that are powered by electricity.
Water distillation
A countertop water distiller uses the highly effective method of distillation to remove TDS from water. During distillation, water is boiled until it evaporates. The majority of total dissolved solids are unable to evaporate with water, and they are left behind in the boiling chamber. Water then condenses into a clean carafe, ready for drinking.
Deionization
Deionization uses an ion-exchange process where water passes through both a positively and negatively charged resin bed, which attracts both cations and anions, removing them from the water and replacing them with ions which forms water molecular. Deionization only works for ionic contaminants, so this process would require the use of another purifier, such as a reverse osmosis system, to remove the non-ionic impurities.
What water treatment technology does NOT reduce TDS?
Water softener
Water softeners work through a process of ion exchange. It will exchange the calcium and magnesium ions in water by releasing sodium ions into water. So theoretically, it does not reduce TDS. In reality, it can even slightly increase TDS.
Activated carbon
Activated carbon works majorly through adsorption. Removal takes place through adsorption phenomena based on surface interactions between contaminants and carbon graphitic platelet surfaces. It is very good at removing organic contaminants, but not as much to the inorganic ions. In most cases, activated carbon filter does not reduce TDS.
Ultrafiltration
Dissolved solids can still pass through ultrafiltration which usually is nominally rated at 0.1nm. An ultrafiltration system does not remove TDS in water.
Beyond TDS
You may want to know other than TDS, what would be a more relevant and easy to measure water quality. Total organic carbon is a measure of the amount of organic compounds contained in a water sample. Organic compounds covers synthetic organic chemicals like pesticide and herbicides and natural microorganism like pathogen carrying bacteria and virus. Organic carbon-containing compounds can either be dissolved in water or exist in water as undissolved, suspended material, or liquid. This organic matter can enter water naturally and through man-made sources/processes. Like TDS, Total Organic Carbon (TOC) is a non-specific indicator. While TDS largely comes from inorganic sources, TOC measures the contamination of organic sources. It is arguably more pertaining in today’s world to pollution and human impact to environment from petrochemicals.