The Multipure Spotlight for September 2020 is “Know Your Contaminants,” which means that this month, our blog posts and social media will focus on the what, why, and how of specific water contaminants and their treatment to make safe drinking water.
Multipure has always focused on treating drinking water contaminants of known concern, whether the contaminants affect the taste or odor of the water or the potential healthfulness of the water. To this end, Multipure filters are tested and certified by NSF International under NSF/ANSI Standards 42 (Aesthetic Effects, e.g., chlorine or chloramine), 53 (Health Effects, e.g., lead, arsenic, or PFOA), 401 (Emerging Compounds/Incidental Contaminants, e.g., estrone, naproxen, or DEET), and P231 (Microbiological Purifier, e.g., bacteria, viruses, or cysts).
In the water treatment industry, the term “TDS,” or “Total Dissolved Solids,” sometimes comes up among consumers, who seek to understand its importance in drinking water contamination and filtration. This may be due to articles spotlighting TDS, or due to water filter marketing focusing on TDS in water. Unfortunately, this can make it more difficult for consumers to understand water contamination and water filtration.
What is TDS?
The term “TDS” stands for “Total Dissolved Solids,” and represents the combined content of all inorganic and organic substances dissolved in a liquid – typically water. For a substance to count toward TDS, they must be small enough to survive 2 micron or smaller pore filtration* (for comparison, Multipure carbon block filters mechanically trap particles down to 0.5 microns, and the average bacteria is 0.2 to 2 microns in size). Common inorganic substances that make up TDS in water include calcium, magnesium, potassium, sodium, carbonates, nitrates, bicarbonates, chlorides, and sulfates. TDS is generally used as a metric for freshwater only, as saltwater’s very nature is high in TDS.
How Is TDS Measured?
TDS is measured either through gravimetric analysis or electrical conductivity, and is reported as milligrams per liter, or mg/L (i.e., milligrams of dissolved solids per liter of liquid); milligrams per liter is also sometimes referred to as parts per million (ppm). Gravimetric analysis involves evaporating the liquid and measuring the mass of residue left – it is considered the more accurate of the two methods, but also the more time-consuming method. Electrical conductivity works on the principle that dissolved solids in the water affect the ability of the water to conduct electricity. A TDS meter therefore measures the electrical conductivity of the water; it is good for providing an approximate value of TDS concentration – up to 90% accurate to the true value of dissolved solids in the water, but not as exact as gravimetric analysis.
How Do Total Dissolved Solids Get in Water?
Total Dissolved Solids enter water sources through agricultural runoff, sewage runoff, mineral-rich earth, and industrial wastewater. Calcium and magnesium are the most common, naturally-occurring elements of TDS.
How Do Total Dissolved Solids Affect Water?
TDS is not considered a primary pollutant, in that it is not generally associated with negative health effects (some research does state that water with little-to-no mineral content can be harmful to general health**). TDS is considered an aesthetic factor in water; minerals such as calcium and magnesium that are the most common contributors to TDS generally have a positive impact on the taste of the water, whose presence contributes to the healthfulness of the water. In fact, mineral water is often specifically purchased due to its higher mineral/TDS content.
Taste studies have set the following aesthetic guidelines when it comes to TDS content in drinking water:
- < 50 mg/L: unacceptable; water tastes flat
- 50-300 mg/L: excellent
- 300-600 mg/L: good
- 600-900 mg/L: fair
- 900-1200 mg/L: poor
- > 1200 mg/L: unacceptable
In the United States, a guideline of a maximum of 500 mg/L has been established for the palatability of drinking water. It is not a legal standard, but more of a general recommendation.
The presence of TDS in water can suggest other technical effects aside from odor and flavor considerations. High concentrations of TDS can produce hard water, which in turn can leave mineral deposits and films on plumbing fixtures, or inhibit the lathering ability of soaps and detergents. High TDS can also stain household fixtures, corrode pipes, and impart a metallic taste to the water.
The primary benefit of TDS in drinking water is the potential presence of minerals that are considered essential to human health. These include calcium, chloride (an important electrolyte for the blood), magnesium, potassium, and zinc.
It is important to note that, although TDS is generally considered a secondary, non-health-affecting water measurement, a high TDS level can be an indicator of the presence of more sinister contaminants, such as lead, sulfate, bromide, or arsenic. This is especially true if the TDS is a result of human, rather than natural, water contamination.
Should TDS Be Filtered from Drinking Water?
Multipure views TDS from a health perspective. TDS is considered a secondary contaminant, whose measurement is not a direct indicator of the potential benefits or harm of the water. As such, Multipure systems treat any TDS filtration as a side-effect of their general drinking water treatment functionality. And while Multipure systems treat the harmful contributors to TDS, such as lead or arsenic, Multipure’s carbon block filters allow healthful contributors to TDS, such as calcium and magnesium, to pass through the filter and remain in the drinking water, contributing to the positive flavor of the water.
Some companies in the drinking water treatment industry tout the necessity of water free of all TDS, akin to “distilled water” or “pure water.” Reverse Osmosis (RO) systems tend to promote this aspect, as RO systems generally result in “flat” water, free of many contaminants, but also free of any beneficial minerals in the water. At least one filtered water pitcher brand specifically markets themselves as a “zero TDS” water filter. At Multipure, we consider this more marketing gimmick than meaningful metric, as studies have shown that some level of TDS is necessary both for the flavor of the water and for the beneficial mineral content in the water.
On the other hand, some parties believe that very high TDS should be encouraged in drinking water. This point of view tends to only look at the positive aspects of TDS (healthful minerals) while ignoring the negative aspects (harmful compounds, damage to infrastructure, etc.). This was highlighted in an episode of the Netflix show, “Down to Earth,” in which a self-appointed “water sommelier” touts the “medicinal benefits” of ultra-high TDS water (in this example, a bottled water with a TDS of 7,400) to actors Zac Efron and Anna Kendrick – an episode that was discussed on a recent Multipure podcast.
Ultimately, Total Dissolved Solids is not really a useful measurement when it comes to the safety of drinking water. While it is generally preferable for water to have a moderate amount of TDS, for aesthetic reasons, and for potential health reasons (if the TDS is contributed by essential minerals), TDS measurement by itself – outside of extremely low or extremely high measurements – is relatively meaningless without additional tests or context. In fact, Multipure released a video demonstrating why TDS is not indicative of the quality of water: https://www.youtube.com/watch?v=d3MCiFB4biE
While some parties may promote TDS as a health hazard, and other parties may tout the wonders and benefits of TDS, the truth is that TDS is simply another way to measure water content, largely separate from any measure of the healthfulness of the drinking water. Any mentions of TDS as a dangerous water contaminant should be taken with a healthy grain of salt, and instead treated as a distraction from more substantial, more hazardous potential drinking water contaminants, like lead, PFOAs, asbestos, and more (all of which are NSF-certified to be reduced by a Multipure drinking water system).
Stay safe, stay healthy, and Taste the Difference of Multipure.
*Butler, Barbara A, and Robert G Ford. “Evaluating Relationships between Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) in a Mining-Influenced Watershed.” March 31, 2018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6020674/.
**Kozisek, Frantisek. “Health Risks From Drinking Demineralised Water.” World Health Organization, 2005. https://www.who.int/water_sanitation_health/dwq/nutrientschap12.pdf.