Certain dissolved substances and microscopic particles are incredibly difficult, if not impossible, to completely remove from water through typical filtration methods. These can include very small ions, dissolved gases, and some extremely fine colloids.
Understanding What Stays in Your Water: Beyond Basic Filtration
When we talk about filtering water, we often think of removing visible impurities like sediment or larger contaminants. However, the world of water purification is complex, and some things are designed to remain, or are simply too small or chemically bound to be filtered out by standard means. Understanding what these are is key to appreciating the limitations of different filtration systems and what truly makes water "pure."
What Are the Unfilterable Elements in Water?
While many filters excel at removing particles, chemicals, and microorganisms, a few categories of substances prove challenging. These are often either too small to be caught by filter pores or are intrinsically part of the water’s chemical composition.
Dissolved Ions and Minerals
Many essential minerals are present in water as dissolved ions. These are charged atoms or molecules that are too small to be physically strained out by most common filters. Think of calcium and magnesium, which contribute to water hardness, or beneficial electrolytes like sodium and potassium.
Reverse osmosis (RO) systems can remove a significant portion of these dissolved ions, but even they are not 100% effective. Specialized ion exchange resins are often used in water softeners to target specific ions like calcium and magnesium.
Dissolved Gases
Gases like oxygen, nitrogen, and carbon dioxide are naturally dissolved in water. These are not typically considered contaminants and are essential for aquatic life. Standard filters do not remove dissolved gases.
In fact, the absence of dissolved gases can sometimes be an indicator of highly purified water, like distilled or RO water, which can taste "flat" to some people. Aeration is a process used to remove dissolved gases if desired, not filtration.
Extremely Small Colloids and Nanoparticles
Colloids are tiny particles that are dispersed in a liquid but don’t dissolve. While many filters can remove larger colloidal particles, some extremely small ones, often in the nanometer range, can pass through even fine filters.
These are generally not a health concern in typical drinking water supplies. They are too small to be seen without a microscope and don’t usually pose a biological risk.
Certain Dissolved Organic Molecules
While activated carbon filters are excellent at removing many organic compounds that cause taste and odor issues, some very small or non-polar dissolved organic molecules can still pass through.
These are usually present in trace amounts and are not harmful. Advanced purification methods might be needed for their removal, but for everyday drinking water, they are generally not a primary concern.
Why Aren’t These Things Filtered Out?
The fundamental reason these substances remain in water relates to their size and chemical nature. Filters work by physically blocking particles larger than their pore size or by adsorbing certain chemicals onto a filter medium.
- Size: Dissolved ions and gases are at the atomic or molecular level, far smaller than the pores of even the most advanced microfilters.
- Chemical Bonding: Many minerals are chemically bonded within the water, meaning they are not separate particles to be strained out.
- Filter Design: Standard filters are designed to remove what’s considered harmful or aesthetically unpleasing, not every single molecule present.
What About Highly Purified Water?
If you’re looking for water with the fewest dissolved substances possible, you’ll need more advanced purification methods beyond basic faucet filters.
- Distillation: This process heats water to steam, leaving impurities behind, and then condenses the steam back into liquid. It removes most dissolved solids and minerals.
- Reverse Osmosis (RO): This forces water through a semi-permeable membrane, blocking a wide range of contaminants, including many dissolved ions. However, it can also remove beneficial minerals.
- Deionization (DI): This process uses ion exchange resins to remove virtually all dissolved ionic contaminants, producing extremely pure water.
Comparison of Purification Methods
| Purification Method | Removes Dissolved Ions | Removes Dissolved Gases | Removes Colloids | Removes Organic Molecules | Typical Use Case |
|---|---|---|---|---|---|
| Basic Filter | Minimal | No | Yes (larger) | Yes (some) | Improving taste |
| Activated Carbon | Minimal | No | Yes (larger) | Yes (many) | Taste & odor |
| Reverse Osmosis | High | Some | Yes | Yes | High purity water |
| Distillation | Very High | Some | Yes | Yes | Lab purity |
| Deionization | Extremely High | No | Yes | Yes | Ultra-pure water |
Common Misconceptions About Water Filtration
It’s easy to assume that any filter will remove "everything." However, it’s important to match your filtration needs to the type of filter you use.
- "Pure" doesn’t mean "mineral-free." Many healthy waters contain dissolved minerals.
- Not all filters are equal. A simple sediment filter won’t remove dissolved chemicals or ions.
- Some things are meant to be in water. Fluoride, for example, is added to many public water supplies for dental health and is not removed by basic filters.
What’s the Takeaway for Your Drinking Water?
For most people, the goal is to have safe, clean drinking water that tastes good. Standard filters, like those using activated carbon, are excellent for removing chlorine, sediment, and many organic compounds that affect taste and odor.
If you have specific concerns about dissolved minerals or want extremely pure water, you might consider a multi-stage system like reverse osmosis. However, remember that removing everything isn’t always necessary or even desirable for taste and health.
People Also Ask
### Does boiling water remove dissolved solids?
Boiling water does not effectively remove dissolved solids or ions. While it kills microorganisms and can help evaporate some volatile compounds, the dissolved minerals and salts remain in the water. In fact, as water evaporates during boiling, the concentration of dissolved solids can actually increase.
### Can a Brita filter remove minerals?
Brita filters, which primarily use activated carbon and ion exchange resin, can reduce some minerals like calcium and magnesium that cause hardness. However, they do not remove all dissolved minerals and ions from the water. Their main function is to improve taste and odor by reducing chlorine and other impurities.
### What is the smallest thing a water filter can remove?
The smallest things that standard water filters can physically remove are typically in the range of 0.5 to 1 micron (micrometer). However, technologies like reverse osmosis membranes can filter down to around 0.0001 microns, effectively removing dissolved salts, minerals, and even viruses. Activated carbon filters work by adsorption, trapping molecules rather than physically blocking them.