Water is one of the most vital substances on Earth!
29 November 2018| Last updated on 6 December 2018
It covers almost 70% of its surface and the human body can contain up to 75% of this liquid.
Water is important in numerous fields including agriculture, science, medical, transportation, food processing and probably most important of all is drinking.
With plastic water bottles and reusable plastic water gallons potentially causing serious risk on one’s health, households are shifting to installing water filters to have access to clean and SAFE drinking water.
But how many types of water filters are there? and how do they work?
There are 5 types of water filters:
- Mechanical Filters
- Absorption Filters
- Sequestration Filters
- Ion Exchange Filters
- Reverse Osmosis Filters
While each of these filters addresses a different water problem, many systems incorporate a combination of these filters to perform multiple levels of filtration.
Mechanical (Sediment) Filters
Sediment filter for mechanical filtration
Mechanical filters are designed to physically remove sediment, dirt or any particles in the water using a barrier. This barrier can be anything from a basic mesh to filter out large debris to a ceramic filter which has a complex pore structure for ultra-fine filtration of organisms like bacteria.
A filter that utilizes mechanical filtration will usually be given a micron rating.
Micron rating indicates how effective the filter is in terms of the size of the particles it can remove. Common ratings include:
- 5 micron – particles visible to the naked eye
- 1 micron – particles too small to see without a microscope
- 0.5 micron – cysts (giardia and cryptosporidium)
Granular activated carbon and carbon block for absorption filtration
Absorption water filters are made of carbon, as it is highly effective at capturing water-borne contaminants. The reason carbon absorbs contaminants so efficiently is that it has a vast internal surface which is full of nooks that can trap chemical impurities like chlorine.
Granular activated carbon (GAC) is the most commonly used in domestic water filters, which reduces unpleasant tastes and odors by absorption.
Different substances can be used to make carbon for filters such as wood and coconut shell; coconut shell being more effective but also more expensive.
Sequestration is the process of chemically isolating a substance, in other word, scale inhibition.
These water filters use food-grade polyphosphate to sequester the calcium and magnesium minerals which cause limescale and corrosion.
However, polyphosphate is generally only introduced in very small amounts and it only constrains scale rather than eliminating it. This means that it does not soften the water but instead works to keep the minerals within the solution, preventing them forming scale on any surfaces they contact.
Scale inhibition isn’t always suitable as hard minerals stay present in the water. Water softening process such as ion exchange is usually recommended instead.
Ion Exchange (Resin) Filters
Ion exchange is a process used to soften hard water by exchanging the magnesium and calcium ions found in hard water with other ions like sodium or hydrogen ions.
Ion exchange consists of resin which normally comes in the form of small beads which physically removes the hard minerals, which in turn reduces limescale and prevents corrosion.
Resins filters that utilize sodium ions increases the amount of salt in water and therefore isn’t used for drinking water. Hydrogen based ion exchange resin is used instead for drinking water filters.
Reverse osmosis (RO) is the process of removing dissolved inorganic solids from the water by forcing it through a semipermeable membrane under pressure so that the water passes through but most of the contaminants are left behind.
Reverse osmosis is a highly effective way of purifying water and is usually combined with several other filters such as a mechanical (sediment) filter and an absorption (activated carbon) filter in order to produce the finest level of filtration for drinking.
Water filters Combinations
Each filter method has limitations on what it can filter-out, therefore, filtration systems use a combination of methods to achieve the level of water purity desired.
For example, Reverse osmosis systems may utilize mechanical, absorption and of course reverse osmosis membrane; depending on how many stages the RO system has.