What’s the Minimum TDS for RO Water?

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Reverse osmosis is one of the most effective water filtration methods out there.

Does that mean there should be absolutely no total dissolved solids left in the water coming out of your RO system? Or is there a minimum TDS level recommended for RO water?

Let’s find out!

Key Takeaways

  • The minimum TDS for reverse osmosis water can be anywhere from 0 ppm to 50 ppm, but it varies depending on feed water conditions and various other factors.

What’s the Minimum TDS for RO Water?

So, what’s the minimum TDS for RO water?

Well one the one hand, if you use reverse osmosis for water purification, you ideally want to achieve 0 TDS, because that means the RO membrane has removed as many impurities as possible (good and bad). This would mean the water is as free from harmful contaminants as possible.

That said, it all depends on the type of dissolved solids in your water. If it’s only calcium, there’s nothing to worry about and a TDS level of 50, 100, or even 150 is perfectly fine. However, if it’s lead, chromium 6, and pesticides, it’s a different story.

Typically, the recommended total dissolved solids level for RO water ranges from 10 to 50 parts per million (ppm), though this estimation can vary due to multiple factors.

The primary factor is the initial TDS level of your feed water. A high feed water TDS may mean a higher TDS in your filtered water, even if the system functions optimally. Other contributing factors include the age and condition of the reverse osmosis membrane and pre-filters, feed water pressure, water temperature, and potential issues with the drain line or flow restrictor.

Reverse osmosis systems can even reach a TDS level of under 25 ppm. While this is an excellent indicator that there are (almost) no harmful contaminants left in your water, it does mean it will have a bland flavor, as the optimal TDS range for flavor and taste in drinking water is 150 ppm or higher.

What’s the Maximum Acceptable TDS Level in RO/Drinking Water?

As per the guidelines set by the World Health Organization, the limits for TDS levels in drinking water are:

  • Less than 300: Excellent
  • Between 300-600: Good
  • Between 600-900: Fair
  • Between 900-1200: Poor
  • Above 1200: Not acceptable

So, you want to aim for your drinking water TDS to be 300 or less.

The WHO provides a TDS number as a guideline for drinking water quality. But again, it’s important to note that the situation is different when it comes to RO water. If your purified water has high TDS levels, it suggests that the RO membrane is not functioning correctly and may still contain harmful contaminants. This can be a problem, indicating the need for replacing the RO membrane.

If you wish to increase TDS levels afterwards, you can consider remineralization. Remineralization involves adding safe minerals to the water, effectively increasing TDS while maintaining water safety.

young woman drinking water

What Is Drinking Water TDS and Why Measure It?

TDS stands for total dissolved solids, which indicates the concentration of dissolved substances in water. It encompasses both harmful contaminants and beneficial ones, such as magnesium and calcium. Reverse osmosis systems excel at eliminating TDS. Their effectiveness is such that running water through an RO system can lead to a 95-99% reduction.

That’s why evaluating the TDS level in the feed water and comparing it to the TDS of the RO water output provides a straightforward method to test if your system is working properly. A functioning reverse osmosis system should reduce at least 80% to 90% in TDS.

Something to note is that TDS levels only indicate the amount of dissolved solids in water, not their specific content (it won’t tell you what kind of TDS you have in the water). So, TDS alone is not a significant indicator of drinking water quality. High-quality water, rich in minerals, often exhibits high TDS levels, whereas water with concerning contaminants may demonstrate a low TDS measurement.

Ideal TDS Levels in Drinking Water

RO water often has a TDS of 10 to 50 ppm, although this can vary. This low TDS means the water won’t taste as nice as water with a slightly higher TDS. In fact, the ideal TDS for drinking water is 150 ppm.

How Does Reverse Osmosis Remove TDS from Water?

Reverse osmosis uses an ultra-fine RO membrane to efficiently remove a significant percentage of TDS ranging from approximately 80% to 99%. The process of RO involves water being forced through the RO’s semipermeable membrane. This membrane has tiny pores that allow the minuscule H20 molecules through, but block dissolved solids and impurities from passing into the filtered water. Instead, they remain on the other side of the membrane and are flushed away with the wastewater.

If you have any questions about the minimum TDS for RO water please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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Leave a Comment:

Jolene Theiss says April 8, 2024

Is it bad to have 15 as the tds number

Reply
    Gene says May 14, 2024

    No!

    Reply
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