Reverse osmosis (RO) water treatment is highly effective at removing toxins, microbes, lead, and debris from water. However, it also removes minerals, which lowers the pH of the water and makes it slightly acidic.
We’ll explore how that change occurs, why it’s important, and how you can test the pH levels of your RO water.
What Makes Water Acidic or Alkaline?
First, we need to discuss what causes different pH levels in water and how this is measured.
Water (H2O) consists of two different ions: free hydrogen ions (H+) and hydroxyl ions (OH-) which also contain hydrogen (H).
Hydroxyl ions (OH- ) can break down into their constituents and produce more H+, affecting water’s potential hydrogen (pH) level.
While the already-present free hydrogen ions determine the water's acidity, hydroxyl ions affect its alkalinity. When they’re equal in number, the water is neutral with a pH level of 7.
The acidity/alkalinity is measured on the potential hydrogen (pH) scale, which tells us the concentration of H+ and OH- ions and how active they are in the water. The more H+, the more acidic the water is, and the more OH-, the more alkaline it is.
Acidity means that the free hydrogen ions inside the water can interact with and corrode surfaces the water comes into contact with. As a result, acidic water can corrode metals and cause stains on faucets, sinks, and appliances.
On the other hand, a higher level of potential hydrogen (pH) means that the water will be less reactive with other elements and compounds it comes into contact with. This is because more hydroxyl ions mean less free hydrogen to react with new substances.
Is Reverse Osmosis Water Acidic or Alkaline?
Reverse osmosis water has a pH of between 5 and 7, which means it’s acidic. This pH level is considered healthy for human consumption.
Here’s a quick breakdown of acidic, neutral, and alkaline water:
Acidic Water
On the pH scale, any substance below 7 is considered acidic.
Acidic water dissolves many substances and has an antimicrobial effect because microbes have more difficulty maintaining their structure inside an acidic substance.
However, because acidic water can dissolve things more efficiently, it often contains more heavy metals like lead, arsenic, nickel, chromium, or zinc, which have severe health effects when consumed.
Neutral Water
On the pH scale, any substance at exactly 7 is considered neutral. Water that has a pH rating of 7 is regarded as pure water because it has an even balance of hydrogen ions and hydroxyl ions.
Alkaline Water
On the pH scale, any substance above 7 is considered alkaline. Alkaline water has less free hydrogen available, so it will not dissolve or react with different substances.
Does Reverse Osmosis Change the pH of Water?
The reverse osmosis process removes certain minerals from water, which changes its natural pH from 6–8 pH to 5–7 pH.
The alkalinity of water relies upon the presence of calcium bicarbonate and magnesium bicarbonate. Without these minerals, the hydroxyl ions will react to carbon dioxide when exposed to air and form more carbonic acids while releasing free hydrogen into the water and lowering its pH.
That said, this process depends on the chemical properties of the initial sample. Therefore, it’s hard to accurately predict how much the water’s pH will decrease after the reverse osmosis process.
Importance of pH for Reverse Osmosis Water
The pH of RO water determines its solubility. It also affects how certain chemicals and heavy metals in the water interact with the biological organisms they’re introduced to.
The solubility of water determines the number of substances it can dissolve. As the pH of the water decreases, more and more elements and chemicals can be dissolved and carried into the water.
Solubility in RO water is necessary to carry healthy nutrients like nitrogen, phosphorus, and carbon. These are essential nutrients that humans and animals need, and they help plants grow too.
However, the same applies to dangerous heavy metals like lead, cadmium, and copper. As they’re in a more dissolved state in low-pH water, they become more toxic for humans and animals.
Since RO treatment removes all these dangerous contaminants, it shouldn’t be a cause for concern.
How to Test the Acidity Level of RO Water
There are different ways to test RO water’s acidity level. It’s best to use the digital pH meter method for the most accurate results.
1. Digital pH Meter:
The steps to follow when using a digital pH meter to test the acidity level of RO water are:
- Attach the digital meter to a container of water that has passed through the RO membrane.
- Press the calibration button and hold it.
- Wait for the digital meter to give you a stable reading.
- Release the button and dry the meter off to use again when needed.
Getting a reading that doesn’t fall within the 5–7 pH range could indicate a problem with your RO treatment system or water source.
2. pH Test Strips:
Using pH test strips is an alternative method for testing pH.
To use pH test strips:
- Take the strips out of the container.
- Dip the strip all the way into the water.
- Shake off any excess water after removing the strip.
- Place the pH strip on a horizontal surface and wait 15 seconds for the strip’s colors to change.
- Compare the changing colors to the chart on your strip instructions to determine the pH reading of your water sample.
3. pH Litmus Paper
Litmus paper is one of the easiest ways to test RO water.
To use pH litmus paper:
- Fill up a clean container with test water. Ensure enough water is in the sample to cover the strip completely.
- Dip the paper into the test container for 15 seconds.
- As you dip the paper, you will be able to observe the paper turning red or blue.
- If the paper turns blue, it is an alkaline solution. If it turns red, it is an acidic solution. If it doesn’t change color, then the sample is neutral.
Conclusion
The RO process removes minerals alongside hazardous contaminants. Removing these minerals means that there are more free hydrogen ions in the water than before, which lowers the pH level from 6–8 to 5–7 and makes the water more acidic.
Acidity in water means that the water is more soluble. Therefore, it can cause corrosion in metal objects and lead to stains on faucets and sinks.
