A question about water filter

The short answer is: If the size of the holes (pores) are too big, the water filter cannot filter out (or trap) the unwanted particles or other chemical or biological substances inside the water. In order to trap these unwanted substances, the holes (pores) have to be smaller than those substances.

The long answer:

First, the reason we use water filters is to filter outparticles and other biological and chemical substances from the water. They are used most commonly to prepare water for irrigation, drinkingwater, aquariums, and swimming pools. Depending on the use, the "size"of the pores within the water filters would vary.

Water filters serve to trap particles and other biological and chemicalsubstances using their small pores. These pores are usually smallenough so that the unwanted substances do not pass through the filter. If the holes(pores) are too big and allow these substances to pass through, thewater filter will then serve no purpose. In order to efficientlyfilter our particles like dirt, bacteria, and other substances, thepores (holes) have to be smaller than those substances.