Everything You Need To Know About Water Treatment Methods
Your Water Is Not the Only Thing That Needs Clarifying
Assuming we’ve already convinced you of the need to filter your tap water, trying to figure out which filtering option is best for you can prove a daunting task. There are hundreds of different water filtration devices out there, and each of them works differently to target specific contaminants. Many factors go into choosing the right filter: your location, your budget, and, of course, the tap which you’ll be sourcing from. But before determining which filtration device is right for you, you’re going to need to learn the lingo. We’ve put together a list explaining the industry’s A to Zs so that you can make your own well-informed decisions.
POE vs. POU Filters
Water filtration systems generally fall under one of two categories: point-of-entry or point-of-use. POE filters (those odd mechanisms underneath the sink that perhaps you’ve always wondered about) connect to a tap source to treat all of the water used in a single home or building. As a cheaper, more easily maintained alternative, POU systems treat the water coming directly from the tap to which they are connected. You can buy or lease a countertop POU system like our Voyager model, or a standalone filtration system like the Pilot. Whichever mechanism you choose, these filtration systems generally prove safer and more cost-effective than drinking tap or bottled water.
The Difference Between Water Filtration & Purification
While the terms are often used interchangeably, water filtration and purification are distinct processes, each using different forms of technology to make water drinkable.
- Water Filtration is essentially a sieving method. A filtration system uses a porous substance to filter out the chemicals and toxins clouding your water, clearing out everything from sediment to bacteria to chlorine. Filters are often discussed in terms of microns, a size measurement of pore size (for reference, one human hair is about 90 microns). The smaller the number, the tighter and more effective the filter. Mechanisms like sediment filters and reverse osmosis systems fall under this general category.
- Water Purification, while often paired with filtration in order to maximize water clarity, refers to water cleaning methods that utilize the chemical properties of different contaminants in order to remove them from your water. Processes like ultraviolet light sterilization and ion exchange are both water purification methods. Activated Carbon filtration uses both standard filtration methods and the chemical process of adsorption in order to decontaminate polluted water.
Neither water filtration or purification alone is sufficient at properly decontaminating your water. Rather, the right combination of both processes will provide you with the cleanest possible water at the lowest possible cost.
Types of Water Filtration & Purification
There are many different types of water filtration and purification that are used in the industry to clear your water of contaminants. We’ve gathered some of the most common processes so that you can understand the magic behind your machine.
#1: Distillation (Mechanical)
- How it Works: Distillation separates contaminants from water by boiling the water and causing it to evaporate and recondense in a separate container while the solid contaminants remain behind.
- What it Removes: Inorganic compounds, most microorganisms, and organic compounds with a higher boiling point than water.
- Advantages: Distillation effectively removes inorganic compounds like lead and nitrate from water, and the boiling process often kills microorganisms like bacteria and some viruses.
- Disadvantages: It removes oxygen and some trace metals from water giving it a flat taste, and requires extremely high levels of maintenance and wastes more water in the process of distillation than it ultimately produces. Distillation has a high energy cost and is not practical for large scale use like home filtration.
#2: Sediment Filters (Mechanical)
There are two types of sediment filters:
- How it Works: Require water to pass through a thick wall of filter material and treatment takes place throughout the depth of the filter. Some depth filters have a “graded density” structure, meaning that the filter gets tighter as the water passes through the filter wall. Graded density filters remove particles of a variety of sizes. The outside catches big particles and the inside holds the smaller ones. Depth filters have more dirt holding capacity, and are usually more effective if a variety of particle sizes are being filtered.
- How it Works: Made in a thin sheet so that only the surface traps particles. These are commonly called “pleated filters” because of their accordion-shaped pleated structure. The pleated arrangement gives the filter surprisingly more surface area than depth filters. One of their great advantages is that they are washable and reusable, more so in large than small micron sizes.
- What They Remove: Most larger suspended solids, such as sediment and dirt.
- Advantages: Necessary to remove larger particles that would damage the fine mesh filter membranes that usually follow. Also decreases water turbidity.
- Disadvantages: Doesn’t remove small or dissolved particles from water; another filtration or purification method must be used along with it in order to properly decontaminate water.
#3: Membrane Filtration
Similar to sediment filtration, membrane filters simply sieve the contaminants out your water using ultra-fine, microporous mesh membranes. Different types of membrane filters vary by pore size (measured in microns – µm) and by the amount of water pressure (and therefore energy) required to push the water through. These filtration systems also vary by flow rate – or the rate at which water flows out of the dispenser once it has been filtered. Because pressurized water is required to generate enough energy to push the contaminated water through the filter, some systems recycle this water back into the system while some dispense it as waste. Therefore, the ideal filtration system has a high water recovery rate which filters the water back into the system. Additionally, an ideal filter has a high flow rate so that it quickly fills your cup of choice.
There are three types of membrane filtration: microfiltration, ultrafiltration, and nanofiltration.
- Microfiltration has a pore size of 0.1-10 µm. It works like a sieve to push water through a fine membrane that leaves large contaminants on the other side.
- What it Removes: Bacteria (Cryptosporidium and Giardia) and suspended solids
- Advantages: Because its pores are relatively large compared to other membranes, it can be operated under low pressures and therefore requires a low amount of energy.
- Disadvantages: The filter requires frequent replacement.
- Ultrafiltration has a pore size of 0.001-0.1 µm. Due to the decrease in pore size, the osmotic pressure required is higher than that of MF.
- What it Removes: Iron rust, sediment, suspended materials, colloid, bacteria, macro-molecular organic matter, silica, viruses, endotoxins, proteins, plastics and smog/fumes such as ZnO.
- Advantages: Mineral elements which are beneficial to the human body can be retained, because the pores aren’t small enough to keep them out. It can be filtered by standard tap water pressure, and has a high flow rate and low cost. Additionally, the recovery rate of water in the ultrafiltration process is as high as 95%.
- Nanofiltration – Pore size of 0.1 nm-0.001 µm. It’s known as the ‘softening membrane’ because it is often used to filter water with low amounts of total dissolved solids and to remove organic matter, softening the water.
- What it Removes: Some salts, synthetic dyes and sugars.
- Advantages: Removes 50% – 90% of monovalent ions such as chlorides or sodium and softens water while retaining healthy minerals like calcium and magnesium.
- Disadvantages: Recovery rate of water is low. That is to say, in the process of making water with nanofiltration membrane, nearly 30% of tap water will be wasted. It is also unable to remove most aqueous salts and metallic ions.
#4: Reverse Osmosis
- How it Works: Reverse osmosis is also a form of membrane filtration, but we’ve given it its own separate section because it is the one most commonly referred to. With a pore size range of 0.0001 – 0.001 µm, it is by far the finest separation material available to date. It is used on a large scale for the desalination and purification of water as it filters out everything except water molecules, with pore sizes approaching the radius of some atoms in many cases. This pore size means it is the only membrane that can reliably filter out salt and metallic ions from water.
- What it Removes: Total dissolved solids (TDS), turbidity, asbestos, lead and other toxic heavy metals, radium, and many dissolved organics. The process will also remove chlorinated pesticides and most heavier-weight VOCs.
- Advantages: It is the most effective mechanical reduction filter, as it filters out pretty much everything except water molecules.
- Disadvantages: The small pore size of RO membranes means that a significant amount of osmotic pressure is required to force filtration. In the process of making water with reverse osmosis membrane, nearly 50% tap water is wasted. It also removes beneficial minerals in addition to harmful ones, leaving the water flat and stripping it of natural healthy qualities.
#5: UltraViolet Purification (Chemical)
- How it Works: Water flows around a clear UV bulb and the light destroys the genetic material of pathogens, preventing them from reproducing.
- What it Removes: Bacteria and Viruses
- Advantages: UV purification is a highly effective treatment for the reduction of microbes and is relatively simple and inexpensive. It adds no chemicals to the water and leaves no by-products. It is very safe and requires little maintenance.
- Disadvantages: Water needs to be mostly clear in order for this treatment to be effective, so it usually has to be filtered by a sediment or membrane filter of some sort before passing through the bulb.
#6: Activated Carbon Filtration
Here’s where it gets a little complicated. Carbon filters come in many different shapes, forms and sizes. They can be infused with sterilizing agents, they can operate mechanically and chemically, they can remove various different contaminants depending on their form, but the bottom line is that activated carbon is the most effective form of water purification out there. Activated carbon is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions to occur. Adsorption is a chemically reductive process that pulls the negative ions out of water using its positively charged surface. These contaminants collect at the surface of the filter and eventually require it to be replaced.
There are four main types of carbon filtration:
Granular Activated Carbon (GAC)
- How it Works: In comparison to powder activated carbon, GAC pores have a larger diameter and are more loosely organized. Modern GAC products are made from coconut shell, coal, wood, lignite and/or petroleum products. They utilize the process of adsorption to pull contaminants out of water.
- What it Removes: Undesirable taste, odor and color, common disinfection byproducts (THMs), organic contaminants like chlorinated solvents and other industrial pollutants, pesticides, herbicides, insecticides, fungicides, algaecides and select heavy metals such as lead and mercury.
- Advantages: High capacity for the reduction of aesthetic contaminants such as tastes, odors or colors. Serve well as pre-filters to carbon block filters or other purifying methods which more effectively decontaminate water.
- Disadvantages: Because they are not tightly packed together, water is easily able to channel through them, reducing its exposure time to the carbon and lowering the rate of adsorption.
Power Activated Carbon (PAC block)
- How it Works: Pulverized carbon is pressed together to form a highly dense, microporous carbon block. This densely compacted block mechanically filters particles down to 0.5 microns, and then utilizes the process of adsorption to chemically pull contaminants out of water.
- What it Removes: Disinfection by-products (DBPs), volatile organic compounds (VOCs), PCBs, MTBE, lead, chlorine, benzene, chloramines, Giardia, Cryptosporidium, asbestos, turbidity, and particulates.
- Advantages: Carbon blocks don’t allow channeling or bypass as easily as GAC filters, allowing for a greater rate of adsorption.
Silver Activated Carbon (SAC)
- How it Works: Carbon is impregnated by silver, which is particularly effective at removing bacterial contaminants. Silver exhibits a self-sterilizing property called the oligodynamic effect that, although not fully understood, is recognized as an effective method for controlling microbial growth.
- What it Removes: Microbes
- Advantages: Sterilizes water using silver at a level 1000 times lower than an amount toxic to humans.
Bead Activated Carbon (BAC)
- How it Works: BAC is made from petroleum pitch and supplied in diameters from approximately 0.35 to 0.80 mm. Its spherical shape makes it preferred for liquidized bed applications such as water filtration. (Liquidized/fluidized bed: A body of solid particles through which gas or liquid is blown or pumped upwards causing separation and movement; a means of increasing reaction rates.)
- High-fill capability: Due to the spherical shape of BAC, it allows you to fill a container or filter with considerably more carbon than with GAC. This increased density extends the life of the filter.
- High Flowability: The beads’ spherical shape allows for a high flow rate without concern for pressure drops. Both air and liquid move freely through the charcoal beads. This allows for complete contact with the entire surface of the beads.
- Low carbon dust: BAC generates less carbon dust due to a bead formation process that does not use binder.
#7: Ion Exchange (Chemical)
There are two types of ion exchange, softening and deionization.
- How it Works: The ion exchange process percolates water through bead-like spherical resin materials (ion-exchange resins). Ions in the water are exchanged for other ions fixed to the beads. Softening is used primarily as a pretreatment method to reduce water hardness prior to reverse osmosis. The softeners contain beads that exchange two sodium ions for every calcium or magnesium ion removed from the “softened” water.
- What it Removes: Calcium, magnesium, lime.
- Advantages: Softens water so that it is prepared for RO and doesn’t damage the filter.
- How it Works: Deionization (DI) beads exchange either hydrogen ions for cations or hydroxyl ions for anions. The cation exchange resins exchange a hydrogen ion for any cations they encounter (e.g., Na+, Ca++, Al+++). Similarly, the anion exchange resins exchange a hydroxyl ion for any anions (e.g., Cl-). The hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion exchanger to form pure water.
- What it Removes: All ions but NOT organic compounds or microorganisms.
- Advantages: Completely purifies water and is better for industrial use or for washing.
- Disadvantages: Resin beds can become medium for bacteria cultures if they are not maintained properly. Additionally, deionization strips water of all its healthy qualities and gives it a flat taste, similar to reverse osmosis.
If you’re still with us, hopefully we’ve demystified some of the most important terms and processes behind water purification treatments. Most purification systems involve multiple processes organized in a specific, harmonious order in order to create the most delicious water possible. Click here to learn more about H2O’s purification process, or sign up for our 7 day free trial to try it for yourself.
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