How to Size a Water Filter: Helpful Information to Know

It’s no surprise that there is far more in your tap water than just water. From heavy metals to buildups of minerals, to dust and dirt, you need the best water filters to make sure pure water is coming into your home. And to get the calcium and magnesium out of your water, you need a water softener. Knowing how to size a water softener filter is easier than you think.

What Are Water Filters?

Carbon water cartridge

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There are lots of types of water filters, and one of the most common kinds is a water softener. The quality of your water differs largely based on where you live and how your water gets to you, but no matter what, there are at least some minerals dissolved in your tap water, making it “hard.” Some of the most commonly found minerals in hard water are calcium and magnesium.

These minerals get into the groundwater when rocks or metals dissolve and travel in the water until it reaches your home. The dissolved solids in your tap water can cause a scaly sort of buildup on everything it touches: your dishes, your appliances, your body, your pipes. Hard water often leads to soap scum and clogged, corroded plumbing. And how to size a water softener filter depends on the kind of water filter you use.

What Kind of Other Water Filters Are There?

faucet water filter

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Another common water filter is the drinking water filter. Having clean, filtered water is one of the most important parts of being healthy. There are water filters that specifically clean your drinking water so you can be sure that you are only consuming purity. These types of water filters are very popular because they are usually cheap and small and can be kept in the fridge. Another popular type of water filter is shower filters. Chlorine is a common substance found in water and removing it can have great health and cosmetic effects.

If you can afford it, one of the best options is getting a whole house water filtration system. While it’s most essential to make sure you are consuming clean water, it’s very beneficial to only have clean, filtered water running through every part of your house. Water softeners that take the calcium and magnesium out of the water for your whole house can improve your life in so many ways. And one of the key parts to successfully installing and caring for a water filtration system is knowing how to size a water softener filter.

Do All Water Filters Work the Same?

Water filter systems come in many shapes and sizes, and they work in many different ways. You may have a preference for what kind of filter to invest in.

Activated Carbon Filters

This type of filter is often known as a carbon filter or pre-filter. Carbon filters are great for removing larger particles, like sediment and silt, from your water. Carbon filters attract and absorb these particles of sediment so they are no longer present in the water that comes out of your tap. They also work to take the chlorine and other contaminants out. Activated carbon filters are also great because they are good at removing the odor and taste from your tap. Depending on where you live, the water that comes out of your tap may be rather stinky. Activated carbon filters will have your water tasting fresh in no time.

Reverse Osmosis

Filters that work through reverse osmosis are extremely popular because the end result is a crisp, clear tap water of outstanding quality. Reverse osmosis filters have a semi-permeable membrane, and pressure is used to force water through the membrane, catching all of the larger contaminants inside.

Alkaline / Water Ionizers

This type of water filter works through a process called electrolysis. This means that the water passes over plates that are electrically charged, and this charge separates the water into two streams. One stream is “alkaline” and the other is “acidic.” The end result is softer water that is very low in acidity and great for your body and skin.

UV Filters

These filters are relatively new on the market. Ultraviolet radiation is used to treat water, destroying bacteria and other contaminants that can be damaging to your health. This type of water filtration system is also extremely popular because it is great for the environment; it doesn’t use any chemicals or additional heat, and gives you water of unmatched purity.

Infrared Filters

This technology is great at softening your water, just like alkaline filters. This is another great option for water softener systems, especially if you live in an area with particularly hard water. This filter uses heat and light to negatively charge the water, giving it a softer feel and smoother taste.

How to Size a Water Softener Filter

When it comes to choosing the right water softener filter, it can be harder than it seems. Many people don’t know how to size a water softener correctly and end up with a model that seems properly sized, but results in a massive salt consumption each year. Knowing how to size a water softener is about more than just the actual size of the system: it’s about efficiency!

Generally, water softeners are sized using grains. Common sizings are 24,000 grain, 32,000 grain, 48,000 grain, or 64,000 grain. To any layman, this seems rather confusing. What does it mean? Well, it’s referring to how many “grains” of hardness your water softener can take out before it needs to regenerate. One “grain” of hardness is 1/7000th of a of a pound of dissolved calcium and magnesium. 

This means that a water softener advertised as a 24,000 grain system should be able to remove 24,000 grains of hardness, or just under 3 and a half pounds of dissolved calcium and magnesium, from your water before it requires regeneration. However, even explained like this, the way capacity is advertised can be misleading when it comes to understanding how to size a water softener.

The reason the way grains of hardness are used to advertise capacity can be misleading is because the advertised capacity is what was reached under ideal laboratory conditions. These conditions include carefully controlled flow rates, water temperature, water pressure, and other conditions that will never be met in the real world. 

How It Really Works

Faucet filtering water because of the installation of water filter

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A 32,000 grain system contains 1 cubic foot of water softening resin, which helps work to remove calcium and magnesium from the water. If you look on the resin manufacturer, they will tell you that 1 cubic foot of water softening resin can remove 32,000 grains of hardness, but only under ideal laboratory conditions. Realistically, 1 cubic foot of water softening resin has a capacity of somewhere around or under 30,000, not 32,000 grains.

But there is something even more misleading when trying to determine how to size a water softener, and that is the amount of salt required during backwash to achieve the maximum capacity. One cubic foot of resin may be able to clear around 30,000 grains of hardness in normal home conditions, but it will need somewhere around 18 pounds of salt to do so! Adding back in that much salt during every regeneration cycle becomes not just frustrating, but costly. Most softeners regenerate about once a week, meaning you’ll have to use almost 1,000 pounds of salt a year!

What most people end up doing is playing around a bit with the recommended salt usage for their water softener. For instance, you may need 18 pounds of salt to regenerate that 1 cubic foot of resin if you want to get rid of 32,000 grains of hardness. But you could also put in just 6 pounds of salt into that same cubic foot of resin, and clear 20,000 grains of hardness. That’s right: one third of the amount of salt will yield two thirds of the maximum capacity. Running your water softener in this method is much more efficient, and easier on your body and your bank account.


Colors playing in water

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Investing in a water filtration system is an important part of valuing the health of you and your family, and it will create a thousand little differences in your home that make you wonder why you waited so long. Water softeners are becoming more and more popular as people become more cognizant of what really is in their water.

But, the discrepancies between the marketing techniques of water softener system manufacturers, and the information they provide on how to size a water softener is misleading to say the least. It results in customer dissatisfaction and a mistrust between the consumer and manufacturer. If you are taking the leap and choosing to invest in a water softener system, be sure you understand the way their capacity is described, and that you are choosing the right option for your family and your home.

For more product reviews, FAQs, and information on everything water softener systems, visit our website today!

Hi I'm Jamie, teacher and owner/chief contributor at We strive to bring you the most informative water filter reviews in the most intuitive and user friendly way. Besides offering advice on the water filter to suit your needs, we also post topical articles on water pollution and the environment. Stay connected and follow us on, Facebook, Twitter, Google+ and more!

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