What’s the pH of Reverse Osmosis Water?

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If you’re considering buying a reverse osmosis system to purify your water, you’re probably interested to know how the reverse osmosis process might affect your water’s pH.

We’ve combined our own knowledge from testing RO systems with data from studies and science papers to help answer the question: “What’s the pH of reverse osmosis water?”

What’s the ph of reverse osmosis water

πŸ“ Average pH of Reverse Osmosis Water

We’ve tested dozens of RO systems ourselves, and we’ve found that the average pH of RO water is typically between 6.0 and 7.0 for systems that don’t use a remineralization filter, and between 7.0 and 8.1 for systems that do remineralize water.

Let’s discuss some of our testing results.

Good to Know: Our tap water’s pH is slightly higher than neutral, reading at around 7.4.

  • After purifying our water in the Waterdrop G3 P800, an under-sink RO system which doesn’t have a remineralization filter, the water’s pH dropped to 6.3; so slightly acidic. View our post-filtration test results here.
  • Water purified in the Waterdrop N1, a countertop RO system that doesn’t remineralize water, had a pH of 7.0; so still in the neutral range. View our post-filtration results.
  • The purified water we dispensed from the RKIN U1, a countertop RO system that does remineralize water, had a pH of 8.1, meaning that the remineralization filter had done a great job of reintroducing minerals and boosting our water’s pH to higher than its original pH. View our post-filtration results.
RO SystempH
Waterdrop G3 P800 (without remineralization)6.3
Waterdrop N1 (without remineralization)7.0
RKIN U1 (with remineralization)8.1

We’ve never tested an RO system that has reduced our water’s pH to below 6.0, but we acknowledge that this could be related to the fact that our water’s initial pH is quite high.

🧐 Is Reverse Osmosis Water Acidic?

Yes, reverse osmosis water is acidic because it typically falls below 7.0 on the potential hydrogen (pH) scale. The pH of reverse osmosis water can drop all the way down to 5, depending on the pH of the feed water.

But reverse osmosis water systems don’t make water dangerously acidic – even the systems that remove all the alkaline minerals from water.

ph scale

πŸ“‰ Why Does Reverse Osmosis Water Have A Low pH?

Two key factors contribute to the reduced pH of reverse osmosis water:

  1. A lack of minerals – Mineral ions such as calcium and magnesium are removed by an RO system. These minerals contribute to water’s alkalinity, so removing them from drinking water decreases its pH level.
  2. Carbon dioxide absorption – Due to its low mineral content, RO water tends to absorb carbon dioxide from the air. When carbon dioxide dissolves in water, it forms carbonic acid, leading to a decrease in pH.

πŸ†š RO Water pH Compared To Other Beverages

How does the pH of reverse osmosis water compare to the pH of other common beverages?

RO water has a lower pH than bottled mineral water and normal tap water, but it’s usually more alkaline than coffee, soft drinks, fruit juice, and sports drinks.

You can compare the pH of reverse osmosis water and other common beverages in the table below.

LiquidAverage pH
Reverse Osmosis (with Remineralization)7-8.1
Reverse Osmosis (without Remineralization)6-7
Tap Water6-8
Mineral Water7.4
Fruit Juice 2-4.5
Soft Drinks2.5
Sports Drinks2.9

πŸ“ Factors Affecting the pH of Reverse Osmosis Water

The pH range of reverse osmosis water can vary due to several factors:

1. The Water’s Initial pH

First, the initial water pH may affect the pH of the purified RO drinking water. If the water is naturally acidic, the RO water pH is likely to have a lower pH.

If the water is naturally more alkaline, its RO pH level is also likely to be higher.

2. The Effectiveness of the RO Process

The efficiency of the RO process and the condition of the semi-permeable RO membrane can also affect the pH of the purified water.

When working optimally, RO systems can effectively remove 90–99% of contaminants, including all dissolved solids. The more effectively the RO unit purifies the water, the more thorough the removal of dissolved substances, and the lower the pH is likely to be.

3. The Presence Of a Remineralization Filter

Some RO systems incorporate a post-filtration step, using a remineralization filter to introduce alkaline minerals back into the drinking water and raising its pH. A 2015 study noted that remineralization can “improve drinking quality significantly” when used post-RO purification.

Whether or not an RO system uses a remineralization filter, and the type and concentration of minerals added back into the water, can impact its pH.

4. Influence By CO2 Absorption

We mentioned earlier that RO water tends to absorb carbon dioxide (CO2) from the air. This leads to the formation of carbonic acid, causing the pH to drop.

So, if you leave your pure water on the side for as little as 1 hour, then test its pH, you’ll probably find that the pH level is lower compared to water that has just been filtered.

πŸ§ͺ How to Test RO Water pH

There are a couple of methods that you can use to test your RO water pH at home:

Use a pH Meter

A pH meter gives the most precise reading of tap water pH.

  1. Calibrate the pH Meter. Follow the manufacturer’s instructions to calibrate the meter using pH buffer solutions.
  2. Collect Sample. Fill a clean container with a sample of your RO water.
  3. Immerse the pH Meter. Immerse the end of the pH meter electrode into your water sample.
  4. Read the pH. Wait for the pH meter to stabilize and provide a reading. The digital display will show the pH level of your RO water.
Taking water ph reading with handheld ph meter

pH Test Strips

pH test strip sets are the cheapest and easiest way to find out where your reverse osmosis water falls on the pH scale. These are widely available and can be bought online for $5-$10 or so for a pack.

  1. Collect Water Sample. Fill a clean container with a sample of your RO water.
  2. Dip the Strip. Dip a pH testing strip into the water for a few seconds.
  3. Wait for Color Change. Wait for the strip to react with the water, causing it to change color.
  4. Match the Colors. Compare the color on the strip to the included color chart (this should come with the test). This will indicate the pH level of your RO water.

Related: The red cabbage test for pH

Testing water acidity with ph test strips

πŸ”Ž How to Make Reverse Osmosis Water Alkaline

There are a few simple ways to boost your RO water’s pH:

Use a Remineralization Filter

The best and easiest way to achieve healthy alkaline drinking reverse osmosis water is with a remineralization filter. These filters can turn your Ro water into alkaline or alkalized water by reintroducing healthy minerals like calcium and magnesium. Some RO systems come with built-in remineralization filters, while for others, these filters are optional add-ons.

Run The Water Through an Alkalizing Pitcher

If you’ve already bought an RO system and can’t add a remineralization stage, consider buying an alkalizing water filter pitcher. You can filter RO water through this pitcher to increase its mineral content and bring it up to an alkaline pH.

Use Mineral Drops

Mineral drops are a budget-friendly solution for increasing RO water’s pH. These add a measured amount of minerals back into your drinking water to support your health. Just follow the manufacturer’s instructions to dissolve these drops into your pure water post-filtration.

πŸ‘¨β€πŸ”§ We’ve discussed these methods in more detail in our guide on the different reverse osmosis remineralization options.

πŸ“‰ Is Low-pH RO Water Bad for You?

Reverse osmosis water is only mildly acidic, so it should have no health effects.

However, according to Healthline, the biggest danger of acidic water (with a pH of 6.5 or lower) is that it might contain high concentrations of metals, since water with a lower pH is more likely to leach metals from its environment. This isn’t usually a problem for reverse osmosis water, which is often produced in a point-of-use system, giving water no opportunity to leach minerals from your home’s plumbing.

Other possible health risks of acidic water include:

  • An increased risk of tooth decay (for water with a pH of 4.5 or less)
  • Bone health effects due to the increased consumption of heavy metals associated with acidic water
Reverse osmosis water has no minerals

RO drinking water is unlikely to cause these health effects because it’s not very acidic and shouldn’t leach metals.

RO water also has a very low essential mineral content. In a 2021 review of existing RO stations, scientists commented that the lack of calcium, sodium, potassium, magnesium, and fluoride in RO water was a “major drawback”, and could cause health issues related to nutrient deficiencies, such as dental decay.

But if you follow a healthy diet that naturally includes these minerals, and use fluoride toothpaste, you shouldn’t experience any of the effects of drinking low-mineral water.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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