Does Tap Water Have Gas in It? The Surprising Science

Over 200,000 chemicals are found in water, but many of the components affecting tap water's look and taste aren't chemicals at all—they're gases. This is because tap water does have gas in it, in the form of naturally occurring dissolved air, a phenomenon responsible for many common water curiosities like cloudiness and flat taste after boiling.

Quick Summary

Tap water contains naturally occurring dissolved gases, primarily nitrogen and oxygen from the atmosphere. These gases often become visible as harmless air bubbles when the water's temperature or pressure changes, resulting in cloudy or milky water that clears from the bottom up. While typically benign, certain naturally occurring or treatment-related gases like methane or hydrogen sulfide can indicate issues and require further investigation.

Key Points

• Tap water contains dissolved gases: Primarily nitrogen and oxygen absorbed from the air, which is a completely normal occurrence.

• Cloudy water is usually harmless air bubbles: A sudden drop in water pressure from the pipes to your glass causes harmless dissolved air to come out of solution, creating a milky appearance.

• Check for air bubbles with the glass test: Fill a glass and watch; if the cloudiness clears from the bottom up within a few minutes, it's just trapped air.

• Boiling water removes dissolved gases: This process is why boiled water has a 'flat' taste compared to tap water, as the gases contributing to the taste have been released.

• Unpleasant odors can indicate other gases: A rotten-egg smell might suggest hydrogen sulfide, while a fizzy appearance in well water could point to methane, warranting professional testing.

• Aeration is a common removal method: For addressing issues with unwanted dissolved gases, aeration systems can mix air into the water to force problematic gases out.

The Hidden World of Dissolved Gases in Your Water

When you fill a glass from the tap and notice it's a bit cloudy, you might wonder what's causing it. The vast majority of the time, this isn't a sign of contamination but rather the result of dissolved gases. Water naturally contains a variety of gases that it absorbs from the atmosphere and surrounding environment. The amount and type of gas depend on a number of factors, including temperature, pressure, and the source of the water.

Water can hold dissolved gases much like a can of soda. When the water is under pressure, as it is in a plumbing system, it can hold more gas. When it's released from the tap, the pressure drops, and the gas comes out of the solution in the form of tiny bubbles. These bubbles scatter light, giving the water a milky or cloudy appearance. As the bubbles rise to the surface and escape into the air, the water in the glass clears, usually from the bottom up. This is the clearest indication that your water is simply full of harmless air.

What Gases Are Hiding in Your Tap Water?

The air we breathe is a mixture of several gases, and since water is in constant contact with the atmosphere, it naturally absorbs these gases. The most abundant dissolved gases are nitrogen (N2), oxygen (O2), and carbon dioxide (CO2).

• Nitrogen (N2): Making up about 78% of the air, nitrogen is the most abundant gas dissolved in water. It is largely inert and has no discernible impact on the taste or safety of your drinking water.
• Oxygen (O2): Essential for aquatic life, dissolved oxygen is a critical component of water quality. It contributes to the fresh taste of water. If you've ever had a glass of boiled water that tastes 'flat', it's because the boiling process removes the dissolved oxygen.
• Carbon Dioxide (CO2): Present in smaller amounts, carbon dioxide can affect the water's pH level. When dissolved in water, it forms a weak carbonic acid. This can cause water to be slightly more acidic and, in higher concentrations, potentially corrosive to pipes.

Beyond these standard atmospheric gases, other gases can sometimes find their way into a water supply, particularly in well water. Methane (CH4), often called 'swamp gas', can be found in groundwater due to the decomposition of organic material. Hydrogen sulfide (H2S), known for its distinct rotten-egg smell, can also occur naturally in groundwater, particularly in low-oxygen environments. While these are less common in treated municipal water, they can be indicators of issues that need to be addressed, such as bacterial activity.

The Impact of Water Treatment and Delivery Systems

Municipal water treatment plants often use aeration as part of the purification process to remove odors and promote gas exchange. Water is also disinfected, most commonly with chlorine, which can also exist in dissolved gaseous forms or as chlorinated compounds. The high pressure in distribution pipes can also cause air to become more dissolved in the water. When this pressurized water is released from your tap into a lower-pressure environment, the gases rapidly escape, causing the cloudy effect.

Is Tap Water with Dissolved Gas Safe to Drink?

For the vast majority of cases where the cloudiness is simply due to harmless air bubbles, the water is perfectly safe to drink. The best way to test this is the glass test: fill a clear glass with water and set it on the counter. If the cloudiness disappears from the bottom up within a few minutes, it was just air bubbles.

However, if you notice other issues, such as a rotten-egg smell (hydrogen sulfide), discoloration, or a persistent, non-clearing cloudiness, it may be time to contact your water supplier or a professional water testing service. A sputtering or fizzy tap is another possible indicator of dissolved gases like methane, which can be an explosion hazard if accumulated in confined spaces, though the risk is mostly limited to private wells.

Tap Water vs. Bottled Water: A Gas Comparison

When you compare tap water and bottled water, particularly carbonated bottled water, the presence of gases is a key differentiator. While tap water contains naturally occurring dissolved gases, carbonated water has had carbon dioxide intentionally added under pressure to create the signature fizziness. Standard bottled water, on the other hand, is not significantly different from tap water in terms of dissolved air, though distillation removes gases entirely, resulting in a 'flat' taste.

Feature	Tap Water	Carbonated Bottled Water	Still Bottled Water	Distilled Water
Primary Gas Source	Atmospheric air, natural sources	Added carbon dioxide	Atmospheric air	No dissolved gas (post-process)
Appearance	Sometimes cloudy due to air bubbles	Always fizzy, visible bubbles	Clear (like tap water)	Clear
Taste	Can vary depending on source; fresh taste from oxygen	Bubbly, acidic taste from carbonic acid	Varies, can be more bland	Flat, no dissolved minerals or gases
Safety	Generally very safe; regulated	Safe to drink	Safe to drink; can vary in quality	Safe; not ideal for drinking long term due to lack of minerals
Cost	Lowest	Highest	Higher than tap	Higher than tap

Dealing with Unwanted Gases in Your Water

If you have identified that your tap water has unwanted dissolved gases, such as hydrogen sulfide or methane, there are several methods for removal. For municipal systems, this is typically handled at the treatment plant. For private well owners, however, treatment may be necessary.

Common methods for gas removal include:

• Aeration: This process involves introducing air into the water, allowing dissolved gases to escape into the atmosphere. Simple aerators for sinks or more complex aeration systems for well water can be used.
• Boiling: As mentioned, boiling water will force out most dissolved gases, which is why boiled water tastes flat. This method is effective for smaller quantities but impractical for household-wide treatment.
• Activated Carbon Filtration: Carbon filters can be effective at removing certain organic compounds and some gases, like hydrogen sulfide, which cause odors.
• Vacuum Degasification: More complex, industrial-scale systems use a vacuum to pull dissolved gases out of the water. This is used in applications requiring extremely pure, gas-free water.

Conclusion: The Final Word on Gas in Your Tap Water

The short answer to the question "does tap water have gas in it?" is a definitive yes. The presence of dissolved gases, primarily nitrogen, oxygen, and carbon dioxide from the atmosphere, is a normal and harmless part of your drinking water. These gases are responsible for the cloudy appearance that often occurs when water pressure changes. Understanding the basic science behind dissolved gases can help alleviate concerns when you see a glass of cloudy water on your counter.

While atmospheric gases are benign, some more concerning gases, such as methane or hydrogen sulfide, can occasionally occur, particularly in well water. For these cases, or for any persistent cloudiness or unusual odors, contacting your local water authority or a certified water testing professional is the wisest course of action. For everyday consumption, however, simply letting a cloudy glass of tap water sit for a few minutes is all you need to do. Enjoy your fresh, naturally gassy, and safe-to-drink tap water.

Frequently Asked Questions

Is cloudy tap water safe to drink?

Yes, in most cases. Cloudy or milky-looking tap water is typically caused by harmless, microscopic air bubbles and is perfectly safe to drink. The best way to check is to fill a glass and watch the cloudiness disappear from the bottom up as the air rises.

Why does my tap water look milky sometimes?

The milky appearance is due to a change in pressure. When highly pressurized cold water comes out of your tap, the dissolved air becomes less soluble and turns into tiny bubbles, which creates the cloudy effect. These bubbles will dissipate on their own.

What kind of gases are in tap water?

The most common gases are nitrogen and oxygen, which are absorbed from the atmosphere. Small amounts of carbon dioxide are also present. Municipal water treatment may also add traces of chlorine for disinfection.

Can dissolved gases affect the taste of water?

Yes. Dissolved oxygen contributes to the 'fresh' taste of water. This is why boiled water, which has had its dissolved gases removed, can taste noticeably flat.

Why do some people with well water experience gassy taps?

Well water can contain naturally occurring gases like methane or hydrogen sulfide from the surrounding geology. A 'gurgling' noise or a 'rotten egg' smell from the tap is a possible indicator of these gases.

How can I remove dissolved gases from my water?

For simple air, waiting a few minutes is sufficient. For more persistent issues like methane or hydrogen sulfide, aeration systems are effective. Boiling water will also drive off dissolved gases.

Is it dangerous to have methane gas in my tap water?

While ingesting methane in water is not considered a health risk, its flammable nature poses an explosion hazard if allowed to accumulate in confined spaces. If you suspect methane, it should be tested and vented properly.