Turn on the faucet, and clear water gushes out—you may have never stopped to think about what this seemingly clean water goes through on its journey from the water treatment plant to your home. China’s tap water is regulated by the *Sanitary Standards for Drinking Water* (GB5749-2022), which covers 106 testing parameters—ranging from microorganisms and heavy metals to organic compounds—providing quite comprehensive coverage. Water that meets these standards when it leaves the treatment plant can indeed be considered safe. But the problem is, the water you drink may not necessarily be the same as the water that left the plant.
The water flowing from your faucet may already be different from what left the treatment plant. Meeting standards at the plant does not guarantee safety by the time it reaches your home. On its journey from the water treatment plant to your faucet, tap water passes through municipal pipeline networks and residential water supply facilities. During this process, there are at least three hidden risks. The first is secondary contamination in the pipes. In many cities, underground water supply pipelines have been in service for over 20 years, and rust and scale buildup on the inner walls of cast iron and galvanized pipes are common occurrences. The longer water remains in the pipes, the more metals—such as iron, manganese, and lead—are leached into it. The phenomenon of “yellow water” in the morning is the most direct evidence of this.
The second risk is secondary contamination from water tanks in older residential complexes. Residential buildings with six or more stories typically require rooftop water tanks or underground reservoirs to provide secondary pressurized water supply. According to regulations, water tanks should be cleaned every six months, but actual compliance varies widely. In tanks with poor seals or those that have not been cleaned for a long time, sediment buildup and microbial growth are not uncommon. The third risk is disinfection byproducts from chlorine. Chlorination of tap water is necessary, but residual chlorine itself has an unpleasant odor. More importantly, when chlorine reacts with organic matter in the water, it produces byproducts such as trichloromethane. National standards set limits for these byproducts, but the actual concentration at the point of use depends on the length of the pipeline network and the residence time—the longer the water “travels” through the pipes, the higher the concentration of byproducts may be.
Using test strips to quickly check your home’s water quality is the first step in determining whether you need a water purifier. Who Really Needs a Water Purifier? Not everyone needs one, but the following four types of households are advised to give it serious consideration.
First, households that prepare infant formula. Infants’ kidneys are not yet fully developed, making them extremely sensitive to sodium, nitrates, and heavy metals in water. Even if tap water meets standards, the cumulative effect of trace contaminants is magnified in infants. Using purified water to prepare formula is the safest choice.
Second, households with elderly family members who have weakened immune systems. Older adults have reduced gastrointestinal function and low tolerance for microorganisms and unpleasant odors; long-term consumption of water containing residual chlorine can easily cause discomfort.
Third, residents living in older housing complexes. In complexes where buildings are over 15 years old and rely on secondary water supply via rooftop water tanks—especially when the frequency of tank cleaning is unknown—the uncertainty regarding water quality at the tap increases significantly. Fourth, residents in areas with high water hardness. In some northern regions, groundwater has high hardness levels and causes severe limescale buildup. Hard water is not necessarily unsafe, but it has an unpleasant taste, shortens the lifespan of appliances, and there is debate regarding the risk of kidney stones associated with long-term consumption. Reverse osmosis water purifiers can effectively reduce water hardness.
Testing tap water with a TDS pen in the kitchen provides a simple and intuitive way to check the readings. In these situations, you actually don’t need to install a water purifier.
Since it’s not an absolute necessity, you can confidently choose not to install one in the following scenarios.
If you live in a newly built community with PPR or stainless steel pipes, the risk of contamination from the water distribution network is extremely low. The new national standards have significantly raised requirements for piping materials; the inner walls of new pipes are smooth, and issues with rust or leaching are virtually nonexistent.
If your home receives direct municipal water supply without a secondary pressurized water tank—meaning water enters your home directly from the distribution network—the absence of the water tank as an intermediate step reduces the risk of secondary contamination. Generally, multi-story residential buildings with six floors or fewer typically use direct water supply.
If you use a TDS pen to measure your tap water and the reading consistently stays below 50, this indicates a low level of total dissolved solids and relatively clean water. In this case, simply boiling the water before drinking is sufficient; there’s no need for additional investment.
💡 A simple rule of thumb: if your new home has direct municipal water supply and a TDS reading below 50—and all three conditions are met—a water purifier serves more to “improve taste” than to provide “safety assurance.” Whether to install one is a matter of personal preference.
Ultrafiltration vs. RO: The Logic Behind the Choice is Simple Once you’ve decided to install a system, the most common question is: Should you choose ultrafiltration or reverse osmosis (RO)? The core difference between the two lies in filtration precision. Ultrafiltration membranes have a pore size of approximately 0.01 micrometers and can trap bacteria, large organic molecules, and some colloids, but they cannot remove heavy metals or dissolved salts. RO membranes have a pore size of 0.0001 micrometers and can filter out virtually everything in water except water molecules—including heavy metals, nitrates, trichloromethane, and calcium and magnesium ions.
The decision-making logic is clear: if your water is hard, poses a risk of heavy metals, or if you have infants or young children at home, choose RO. The water produced by RO is close to purified water, with TDS levels reduced to below 10, making it safe for preparing infant formula or drinking directly. The drawbacks are that it requires electricity, produces wastewater (with a purified-to-waste ratio of approximately 1:1 to 3:1), and has a relatively slow flow rate. If your goal is simply to remove residual chlorine and unpleasant odors, improve taste, and your TDS level isn’t high to begin with, ultrafiltration (UF) is sufficient. UF requires no electricity, produces no wastewater, and delivers a high flow rate, filtering out bacteria and suspended solids while retaining minerals. However, keep in mind that UF cannot reduce water hardness or remove heavy metals—don’t harbor any illusions about this.
RO (Reverse Osmosis) water purifiers offer the highest filtration precision and are suitable for households with poor water quality or those with infants and young children. Here are three tips to assess your home’s water quality: Instead of relying on hearsay, use actual test results as your guide. With just three inexpensive tools, you can get a clear picture of your water’s condition.
Tip 1: A TDS pen. Priced at 20 to 30 yuan each, simply dip it in water for 3 seconds to get a reading. TDS measures the total dissolved solids in water; the lower the number, the “purer” the water. Municipal tap water typically has a TDS level between 100 and 300; if it exceeds 400, you should take note. While TDS cannot detect bacteria or residual chlorine, it serves as a very practical baseline reference.
Tip 2: Residual Chlorine Test. Purchase residual chlorine test solution or test strips to measure residual chlorine levels in just a few minutes. High residual chlorine levels indicate that organic matter hasn’t reacted fully with the chlorine, or that the water has been sitting in the distribution system for too long—which increases the risk of disinfection byproducts.
Tip 3: Check for scale. The most straightforward method: Is there white scum floating on the surface of boiled water? Is there a thick layer of scale buildup at the bottom of the kettle? A lot of scale indicates high levels of calcium and magnesium ions, meaning the water is hard. For severe hardness issues, a reverse osmosis (RO) water purifier is the most effective solution.
A TDS pen, residual chlorine test solution, and hardness test strips—the entire kit costs less than 100 yuan.
📌 Summary
National standards for tap water are very strict, and water leaving the treatment plant is safe. However, between the water treatment plant and your home faucet, three risks—pipe corrosion, water tank contamination, and disinfection byproducts—cannot be ignored.
Households with new homes, direct water supply, and low TDS levels may not need one; however, installation is recommended for older neighborhoods, households with infants or young children, and those with high water hardness. Ultrafiltration improves taste, while RO provides comprehensive purification—which one you choose depends on your household’s actual water quality.
Instead of agonizing over whether to install a system, why not spend a few dozen yuan on a TDS pen to test your water first? Data is more convincing than anxiety.
