Microns: Measuring Water Filter Effectiveness

Whole house water filter systems are used in homes throughout the world. These filters trap harmful and unpleasant substances in the water you use to drink, bathe, and cook meals. Every filter is different, and its effectiveness depends on the microscopic pores in the filter elements, which are measured in microns. What size of microns should your whole house water filter have to ensure pure, clean, fresh-tasting water? In the following guide, we will explore water filter micron sizes, giving you the details you need to select the best whole house water filter system for your needs.

What is a Micron?

A micron is a unit of measure that equals one-millionth of a meter (0.0000001 m). The unit is sometimes referred to as a micrometer, and its symbol is often represented as “mu” or µ. Scientists use microns to measure the wavelengths of radiation as well as the dimensions of organisms like bacteria and cells. To put into perspective how small one micron is, consider:

• A piece of plastic kitchen wrap is about 10-12 microns thick.
• A human hair is about 100 microns in diameter.
• A droplet of water in clouds or mist is about 10 microns in size.
• A bacterial cell may range from 1-10 microns in size. 

As you can see, a micron is a tiny measurement. A pore with a diameter of one micron would be invisible to the naked eye in a water filter. So too are the substances these filters trap from drinking water supplies. Any particle smaller than 35 microns in size cannot be seen without magnification.

Micron Water Filters

In a water filtration system, the microscopic pores of the filter are designed to trap particles from water supplies, leading to fresh, pure water. Whole house water filter systems are sometimes referred to as “micron filter” systems. The smaller the micron rating, the finer of particulates and contaminants removed from the water. Water filters are rated individually, with 0.1 microns, .5 micron, 5 microns, and 10-micron filters commonly found on the market.

Many whole house water filter systems use multiple filter elements or cartridges, each with its micron rating. Filter cartridges with larger micron ratings – 5 to 10 microns -- trap sand, sediments, and silt before the water passes to the next element. The next filter element may be rated at one micron, trapping smaller particles like salts, bacteria, and protozoic cysts like Giardia. In some areas, dirt particles may be so small that they pass through the first stage; the second or third stages will trap them.

Final filter elements in whole house water filter systems may combine an element rated at 0.1 microns with another filtration medium like activated carbon. These final stages nearly everything that passes through the first two filter stages, leaving the water fresh and pure. 

Nominal vs. Absolute Micron Filters

As you shop for a whole house water filter system, you may run across terms like nominal micron and absolute micron. The difference is in the filter’s effectiveness. A nominal micron filter – let’s use a 5-micron filter for an example – may allow a small percentage of particles measuring 5 microns through the filter pores. On the other hand, an absolute micron filter traps at least 95% of the particles it is rated for. An absolute rating is almost like a guarantee that particles of a certain size will be filtered from the water supply. Most water filter systems are equipped with nominal micron filters, but absolute micron filters are available for the cleanest water used in some residential and commercial applications. 

How Do I Know When My Micron Filter Needs to be Replaced?

Whole house water filter systems are used to ensure safe, clean drinking water in the home. These filter systems process thousands of gallons of water before the filter elements need to be replaced. Over time and through use, the pores in the filter elements become clogged with microscopic particles. A symptom of a filter that needs replacing is when the water pressure drops to an unsuitable level. If your filtered water trickles out of the system, that’s a good sign your filter elements need replacing.