At What TDS Level Is RO Required?
Written by: Gene Fitzgerald // Last Updated: Aug 2, 2023
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Reverse osmosis water systems effectively filter, well, almost everything. This includes total dissolved solids (TDS).
However, the level of TDS in (municipal) water is often not considered unsafe.
So, is there a measure of TDS in water that indicates you should be using a reverse osmosis system? Let’s see.
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Key Takeaways
- Reverse osmosis or water filtration that reduces TDS is necessary when the TDS concentration reaches 1,000 ppm, according to the EPA, or 1,200, according to the WHO.
- The EPA suggests a TDS of 500 ppm or less as generally safe.
- The “ideal” TDS in drinking water for taste is around 150 ppm.
At What TDS Level Is RO Required?
At what TDS level is RO required?
The Environmental Protection Agency (EPA) suggests a TDS concentration of 500 parts per million (ppm) in water is acceptable. They also warn that concentrations surpassing 1,000 ppm could pose potential risks. In contrast, the World Health Organization (WHO) stipulates that any water exhibiting a TDS concentration exceeding 1,200 is deemed unsuitable for consumption and filtration is required.
It is also important to try and establish what kind of TDS you have in your water with testing. For example, water from mineral springs may have a high TDS level but caused by healthy minerals. Or the TDS could be elevated with dangerous contaminants. Knowing what your total dissolved solids actually are might be a sign that a filtration system is necessary even before the TDS reaches levels considered to be unacceptable.
Generally, once water has been filtered through a reverse osmosis system, the TDS will typically range from 10-50 ppm, and it is not required to be zero. The actual TDS level of RO water may vary as it largely depends on factors such as the TDS of the feed water, water pressure, temperature, and the condition of the RO membrane.
Standards for TDS Levels in Drinking Water
TDS levels can fluctuate depending on the origin of your water. The TDS levels in tap water may range from 200 to 1,000 ppm or more, depending on the water source. Areas with elevated mineral concentrations may experience substantially higher TDS values in their water supply.
For the best tasting drinking water, aiming for a TDS range of around 150 ppm is recommended, which is higher than the TDS found in RO water. One way to address this is by adding a remineralization filter stage to your RO system. These filters help restore beneficial minerals such as magnesium, calcium, and potassium that may have been removed during earlier filtration stages. As a result, the TDS and mineral content of the RO water increase, leading to a more well-rounded flavor.
Safe and Unsafe TDS Levels
The WHO conducted a study to establish the ideal TDS level ranges in drinking water, with the findings as follows:
- 50 – 300: Excellent
- 300 – 600: Good/Acceptable
- 600 – 900: Fair
- 900 – 1,200: Poor
- Above 1,200: Unacceptable
Further Reading:
What Are Total Dissolved Solids and How Do You Measure Them?
Total dissolved solids is an umbrella term encompassing a range of organic and inorganic matter, varying in size. Some of these include heavy metals, minerals, salts, pesticides, and water disinfectants. TDS levels solely measure the overall dissolved solids in water but do not indicate what those TDS might be. It could mean elevated levels of compounds harmful to health or high levels of calcium and magnesium etc. that are beneficial.
Rock formations are the primary source of TDS in drinking water. Water absorbs minerals through prolonged contact with mineral-rich rocks, resulting in a TDS level of around 400 to 650 ppm. Although this level may be higher than other water sources, the dissolved substances mainly consist of essential minerals, making it safe. However, some sources of TDS can be from sewage, agricultural runoff, storm overflow, industrial and chemical runoff, or pipe leaching, which is more concerning.
Measuring total dissolved solids in RO water is usually done using a TDS meter, which is probably the easiest method, or using filter paper.
How Does Reverse Osmosis Filter Out TDS?
Reverse osmosis filters out total dissolved solids levels by pushing water through the RO membrane. This membrane has tiny pores, which allow only tiny molecules to pass through, leaving the TDS to be flushed away with the wastewater.
Typically, RO systems can eliminate approximately 80% to 99% of dissolved solids, ensuring a highly purified end product.
If you have any thoughts about the question, at what TDS level is RO required, please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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