Water Filters That Lower pH – And How They Do It!

Before you take a drink of filtered water, you probably want to know if the water is acidic or alkaline. Especially, since some water filters or purifiers can change the pH of your water.

Distillation and reverse osmosis lower the pH of water. The purification process removes contaminants from the water altering the pH. The treated water then absorbs carbon dioxide. This reacts with the water to form carbonic acid and lowers the pH of water, making it more acidic.

As a geoscientist, chemical research is one of my favourite things. So to answer this question I decided that, like me, you would probably want to know more than just whether or not water filters can lower pH!

This post explains what pH is and which water filters lower the pH of water, and also how they do it. PLUS the different methods you can use to increase or decrease the pH of water yourself.

Do water filters lower pH?

Before we delve into whether or not water filters lower pH, it’s important to understand what pH is exactly.

Well, pH technically stands for “potential of hydrogen”, but that really isn’t a very helpful explanation. So, I am going to try and explain what pH is without using completely unhelpful science jargon.

pH is essentially a scale that goes from 0 to 14 and is used to rank how much available hydrogen ions there is in a water-based liquid (also known as an aqueous solution). I say ‘available’ hydrogen, because it is available (or free) to combine with other things in water to form acids.

So, it is hydrogen ions that can make water either acidic or alkaline.

  • Acidic water has a low pH because it has lots of free hydrogen ions
  • Alkaline water has a high pH because it doesn’t have many free hydrogen ions.
  • Neutral water has a pH of 7 and sits in the middle of the scale just like Goldilocks’ porridge.

Ok, now that we have covered what pH really is (just a number that tells you whether something is acidic or alkaline), let’s get back to the actual question we are here for…

Do water filters lower pH?

Most filters and purifiers have no effect whatsoever on pH. But there are 2 water filtration or purification systems that can lower the pH of water.

The 2 water purification systems that do lower pH are:

  1. Distillation
  2. Reverse Osmosis

Faucet-mounted and gravity-based filters, Ultrafiltration and Ultra Violet systems will not lower the pH of water.

Even though distillation and reverse osmosis purify water in two totally different ways, HOW they lower the pH of water is the same.

First, let’s talk about how each system works:

1. Distillation

A standard distillation system purifies water by boiling the water. The steam is captured and then cooled until it condenses back into liquid water.

Distillation treats the water, because when the water evaporates (turns to steam) the bacteria, metals, minerals and chemicals in the original water are left behind.

The cooled liquid water is free from contaminants and ready to drink!

2. Reverse osmosis

A reverse osmosis system has a slightly more complex set-up. It uses multiple stages of filtering to treat water.

A reverse osmosis system can have as many as 6 stages, but the important stages are:

  1. Pre-sediment filter
  2. Carbon filter
  3. Semi-permeable membrane

The pre-sediment filter is self-explanatory – it removes sediment! That’s the visible particles in the water, like dust, dirt or sand.

The carbon filter removes chlorine and other things that affect the taste or odor of the water, like organic compounds.

But, it’s the semi-permeable membrane that does the grunt work of the purification system. The membrane removes the bacteria, metals, minerals and chemicals that contaminate the water.

How does distillation and reverse osmosis lower the pH of water?

Distillation and reverse osmosis are both so effective at removing contaminants from water that it can cause the pH of the water to eventually reduce.

I say eventually because in actual fact, immediately after distillation and reverse osmosis the pH of the treated water is usually around 7 – perfectly neutral!

But, after the water is purified it comes into contact with the air around it. Now, air contains several things, including oxygen, nitrogen, argon and most importantly carbon dioxide.

The water absorbs some carbon dioxide from the air, which then reacts with it to form:

Carbonic acid!

And, if you add acid to water it will lower the pH.

It takes around 2 hours for water to absorb all the carbon dioxide that it can from the air (this is when water had established equilibrium). When it has finished the water will have a low pH and be acidic.

This decreased pH also results in increased corrosivity of the treated water. In fact, the water can be so corrosive that it can leach metals, such as copper and lead, from your pipes into your water.

In some cases the water will have to be treated again to raise the pH – keep reading to find out how this is done.

What is the best pH for drinking water?

Pure drinking water should ideally have a pH of 7.

A pH of 7 means that there isn’t anything in the water making it either more acidic or alkaline. But this is also almost impossible to get in the real world. Things like minerals or chemicals are usually present in water to some degree.

The Environmental Protection Agency (EPA) recommends water should have…

“… pH levels of between 6.5 and


environmental protection agency

This range is still considered ‘neutral’ on the pH scale, which means it is still great for drinking and is not acidic or alkaline.

When the pH of water is lower than 6.5 it is acidic and can be corrosive. In fact, the lower the pH, the more corrosive the water is.

Acidic water can corrode the pipes in your home, leaching metals into your drinking water. Metals such as:

  • Copper
  • Iron
  • Lead
  • Zinc

This can make your water taste salty or metallic, or even look rusty.

Not only that, exposure to water with a pH of 4 can cause red and irritated eyes and at pH of 2 damage to our outer layer of skin is permanent!

A pH above 8.5 means the water is alkaline. Many people suggest that high alkalinity does not pose a health risk. However, this is not exactly true.

The World Health Organisation (WHO) says that people exposed to water with pH greater than 11 can experience

“… irritation to the eyes, skin, and mucous membranes”.

workd health organisation

Gastrointestinal irritation can also occur and even hair fibres can swell!

If you want to know what the pH of your water is you can buy some pH measuring strips from Amazon for just a few bucks. Unfortunately, there is a reason why they are so cheap – they often don’t work. The colors run and make it hard to read the pH.

A better alternative, and easier to use, is a digital pH meter. I use a digital meter in the lab all the time. You do have to calibrate it, but the meter comes with everything you need to do this. This is the best one available on Amazon.

It is still inexpensive, but it’s also accurate – and far better than measuring strips! – And the calibration process is easy, the pH meter just needs to be told what different pH’s are by using buffering solutions. Once calibrated the pH meter can read the pH of your water easily and accurately.

How to lower the pH of tap water

It’s important to remember that alkaline water, which is water with a high pH, is not good for us.

Acid injection and anion exchange can lower the pH of water. They are the only deliberate and controllable methods of reducing the pH of water. Distillation and reverse osmosis can lower the pH of water, but as a by-product of the purification process and is not a controllable method.

  1. Acid injection
  2. Anion exchange

1. Acid injection

This is the simplest and most cost effective method of lowering the pH of water.

Acid injection uses a chemical feed pump to release an acid solution into water. The acid solution is injected directly into the alkaline water to lower the pH.

The most common acids injected are:

  • Aluminum sulfate (also known as Alum)
  • Acetic acid (also known as white vinegar!)
  • Citric acid

Unfortunately acetic and citric acid can also leave an unpleasant taste in the water after treatment.

Sometimes a qualified person will use sulfuric acid or hydrochloric acid to lower the pH of water.

However, sulfuric or hydrochloric acid is typically only used when the pH of the water is really quite high, with a value between 11 and 14.

2. Anion exchange

During anion exchange, water flows through a resin. The resin contains an ion that exchanges (or swaps) with the ions already in the water that are responsible for the high pH.

The ion in the resin is usually chloride.

The chloride exchanges with the alkaline components of the water – most of the time these are:

  • Bicarbonate
  • Carbonate
  • Sulfate

By removing these components from the water the pH is lowered.

An added bonus of an anion exchange system is that the EPA has identified them as the…

…“best available technology”(BAT)

u.s. environmental protection agency

for the removal of

“… radium, uranium, gross alpha, and beta particle and photon emmiters”.

U.S. environmental protection agency

This is because the anion exchange system doesn’t just swap out the alkaline components in the water but also other components, including silica.

Anion exchange systems are point of entry devices that can easily be purchased and installed.

How to increase the pH of water

Neutralizing filters, neutralizing solutions and water ionizers are the best ways to safely increase the pH of your water. However, it is important to remember that alkaline water can be harmful to drink. Always make sure that your water’s pH is within the range recommended by the EPA (pH of 6.5-8.5).

Before you decide which one is for you, here is some more information about each method:

1. Neutralizing filter

Neutralizing filters are really effective at increasing the pH of drinking water.

These filters contain either calcium or magnesium, which they release into the water as it flows through.

When the pH is greater than 6 the neutralizing filter will usually release calcium carbonate to raise the pH, and when it is lower than 6 it will release magnesium oxide.

Neutralizing filters are useful if you have acidic water that you want to make drinkable. They can even be bought as add-on options to existing water filter or purification systems, like a reverse osmosis system.

BUT, you should also know that this neutralization process can sometimes increase the hardness of your water. This is because high concentrations of calcium and magnesium make water ‘hard’.

2. Neutralizing solution

A neutralizing solution is a great idea if you have large quantities of acidic water. You can still use it on smaller amounts of water, but a neutralizing filter would be more appropriate.

Neutralizing solutions contain a compound that is able to increase the pH of water. Typically, the compound is either

  • Soda carbonate (also known as sodium carbonate)
  • Sodium hydroxide
  • Potassium carbonate

Although, soda carbonate is more common.

The neutralizing solution is fed directly into the water system. This is usually done by a chemical feed pump injecting the compound directly into the water stream.

This solution is able to raise the pH of acidic water with a pH as low as 4!

Because the solution is so powerful it is really important that the neutralizing feed solution is maintained at exactly the designated level. Otherwise it is possible for the water to become too alkaline, which can be harmful and as we discussed earlier.

3. Water ionizer

Water ionizers are really neat appliances that you can use to increase the pH of water.

A water ionizer uses electrolysis to separate the acidic and alkaline components within water.

While the components themselves are not truly acidic or alkaline, once they come into contact with water molecules they can become acidic or alkaline.

Acid forming components are often:

  • Chlorine (can form hydrochloric acid)
  • Fluoride (can form hydrofluoric acid)
  • Sulfur (can form sulfuric acid)

Alkaline forming components are often:

  • Calcium (can form calcium carbonate)
  • Magnesium (can form magnesium oxide)
  • Potassium (can form potassium carbonate)

So, the water ionizer separates out these alkaline and acidic components – essentially making 2 streams of water, and the alkaline portion of the water can then be used for drinking. This is because the pH of this water is now higher (but within a drinkable range)

In fact, an ionizer can increase the pH of water up to as high as 9!

The great thing about water ionizers is that the acidic portion of the water is not wasted. This water can still be used for things other than drinking, like washing or watering.

Water ionizers can be outrageously expensive, well beyond $3000. But, you can actually get an ionizer for under $800 from Amazon. Don’t worry they also sell the really expensive ones if that’s what you prefer!

I would recommend this water ionizer (Amazon link). It has really good reviews and the company has a great customer service record. It looks to me like they really stand by their product.

Related Questions

What is alkaline water? Alkaline water is technically water with a pH greater than 8. However, the ‘alkaline water’ that is marketed as a health product, is water that usually does not only have a high pH, but also contains alkaline minerals. These minerals usually contain calcium, magnesium or potassium.

What is the pH of bottled water? The pH of bottled water can vary substantially. Bottled water manufacturers do not need to disclose the pH of their water. However, studies have revealed that most bottled water has a pH between the EPA recommended range of 6.5 to 8.5. Most sit on the lower end of the scale between 6.5 and 7.5. Although, in some studies a few brands have recorded ph levels as low as 4.

What are pH drops for water? Liquids advertised as ‘pH drops’ are actually mineral drops. The solution contains minerals, like calcium, magnesium or potassium that aim to increase the pH of water, to make it alkaline. Manufacturers of pH drops frequently claim that they are able to turn water into antioxidant rich water.

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