The Purification Principle of Reverse Osmosis Water Filters and Nutritional Insights on Purified Water

The Purification Principle of Reverse Osmosis Water Filters and Nutritional Insights on Purified Water

In recent years, drinking water safety concerns have frequently made headlines, fueling the popularity of water purifiers.

Yet when considering purchasing a water purifier to combat “contaminated water,” many worry that the filtered purified water may be detrimental to health. Amidst a barrage of news reports and misinformation, ordinary consumers find themselves overwhelmed.

To address this, we'll tackle three key questions: explaining purification principles, guiding you in selecting a water purifier suited to your needs, and clarifying whether purified water truly lacks nutrients.

Question 1:

Some believe that regularly drinking “pure water” from water purifiers can harm your health. To cater to this perception, manufacturers have launched products that supposedly “retain minerals.” Is drinking mineral water really better than pure water? Can drinking pure water lead to malnutrition?

Rebuttal:

The Chinese Dietary Reference Intakes (2016 Edition) recommends daily intake of macronutrients (e.g., calcium, phosphorus, potassium) and micronutrients (e.g., iron, copper, manganese), which are essential for building body tissues and maintaining physiological functions.

　　Unfortunately, current separation technologies struggle to completely distinguish these beneficial elements from toxic heavy metals like mercury, lead, and cadmium. If you aim to retain everything, you must filter everything.

When shopping for water purifiers, you'll notice mineral-focused models typically cost under a thousand yuan, while pure-water systems often exceed several thousand yuan.

　　In reality, mineral-focused purifiers primarily employ lower-grade, cost-effective ultrafiltration or nanofiltration membranes as their core filtration components. Manufacturers often omit that this approach retains not only minerals like calcium, phosphorus, and potassium but also harmful substances such as mercury, lead, chromium, and cadmium.

　　Regarding concerns about nutritional deficiencies from drinking purified water, Zhang Nengwei, Vice President of Beijing Century坛 Hospital, has publicly stated: “The primary source of nutrients for the human body is food. Nutritional deficiencies in people who regularly drink purified water have absolutely nothing to do with the water itself.”

Furthermore, Take “calcium” as an example. The daily reference intake for calcium listed in the manual is 800 milligrams. Most commercially available mineral waters contain 4 milligrams of calcium per liter. If an adult drinks 2 liters of water daily, they would only obtain 8 milligrams of calcium from water. In contrast, 1 liter of milk contains as much as 1,000 milligrams of calcium; a serving of stir-fried black fungus with eggs provides over 500 milligrams. Therefore, for someone with a normal diet, drinking water primarily serves metabolic functions. Relying on water to supplement trace elements is less effective than inhaling a few breaths of smog.

▲100ml of milk contains 120mg of calcium

In summary, consumers are advised to choose water purifiers based on their specific local conditions.

Question 2: Is it reliable to select a water purifier based on a TDS pen that costs around twenty yuan with free shipping?

Science Explained: Pure water without impurities is nearly non-conductive. Water conducts electricity because it contains conductive impurities.

The TDS pen measures water conductivity to estimate the total dissolved solids (TDS) by calculating the concentration of all dissolved charged particles.

Theoretically, a lower TDS value is better, indicating fewer conductive impurities in the water. However, it's important to note that TDS does not reflect the presence of non-conductive substances like bacteria and organic matter. Therefore, a low TDS value only partially indicates good water quality.

A high TDS value requires further examination. As mentioned earlier, conductive “impurities” can be beneficial or toxic. Some water may contain essential elements for the human body, which are conductive and thus raise the TDS value. Conversely, water containing toxic impurities will have an unfavorably high TDS value.

　　In summary, TDS pens are suitable for preliminary household water quality analysis but provide imprecise readings. Certain contaminants (e.g., bacteria, organic matter) do not elevate TDS levels. Consumers with tap water TDS values exceeding 100 are advised to consider reverse osmosis water purifiers.

Question 3: Why do reverse osmosis water purifiers require electricity and produce a certain percentage of wastewater? What is the principle behind reverse osmosis water purification?

Answer: Let me pose an interesting question first: Seawater is undrinkable, yet seagulls fly over the ocean—what do they drink?

The answer is seawater. Seagulls possess a membrane that filters impurities from seawater. Humans have replicated this principle to create reverse osmosis membranes.

Originally designed for space travel when limited technology prevented carrying large drinking water supplies, reverse osmosis purifiers were used to recycle urine and wastewater for drinking purposes. Interestingly, the treated sewage water Bill Gates famously drank also utilized reverse osmosis membrane filtration!

Since pressurization is required, reverse osmosis purifiers need to be powered by electricity. The concentrated wastewater produced is undrinkable and is referred to as effluent; it can be used for tasks like washing clothes or mopping floors.