Air bubbles leave water when you give dissolved gas a reason to come out of solution and a path to escape. The simplest approach for a glass of drinking water is to let it sit at room temperature or warm it gently, but the best method depends entirely on why the bubbles bother you. A home brewer trying to avoid off-flavors, a laboratory analyst running sensitive instruments, and a facilities engineer protecting boiler tubes all need different levels of degassing, and the techniques range from a kitchen kettle to hollow-fiber membrane modules that strip oxygen down to parts-per-billion concentrations.
Why Air Gets Trapped in Water
Water at room temperature and normal atmospheric pressure holds a surprising amount of dissolved gas. Cold water holds even more, which is why a glass of cold tap water develops tiny bubbles on the inside of the glass as it warms up: the water becomes slightly oversaturated for the new temperature and the excess gas nucleates on microscopic imperfections in the glass. Pressurized municipal water lines compound the effect. When water travels through pipes under pressure, it can absorb more gas than it would at atmospheric pressure. Open the tap and the pressure drops, so some of that dissolved air forms visible bubbles almost immediately.
There is an important distinction between visible free bubbles (the ones clinging to your glass) and dissolved gas that remains invisible in solution. Most household complaints involve free bubbles that form after a pressure or temperature change. Most industrial and scientific concerns involve dissolved gas that never forms a visible bubble but still causes problems, whether that is corrosion inside a boiler, detector drift in a chromatograph, or cloudy ice cubes. The removal strategy differs accordingly: free bubbles can often be coaxed out with gentle agitation or patience, while dissolved gas requires more aggressive physical or chemical intervention.
Letting Water Stand or Stirring It
For everyday situations, the easiest fix is time. Fill a pitcher, leave it on the counter, and the tiny bubbles that formed when the pressurized tap water hit atmospheric pressure will gradually rise to the surface and pop. Gentle stirring speeds things up by giving the bubbles a nudge. This works fine for drinking water that looks milky-white after pouring, a common sight in cold weather when the water is especially gas-rich. The cloudiness clears from the bottom of the glass upward as microbubbles float out, and it usually takes less than a minute.
Stirring or swirling also helps when you are mixing something and air gets whipped in. Think of pancake batter or a freshly mixed epoxy: tapping the container on a hard surface encourages trapped pockets to rise. For thin liquids like water, this is sufficient. For thicker materials, it is not, and we will get to why shortly.
Boiling
Heating water drives dissolved gas out because gas solubility in water drops as temperature rises. Boiling is the brute-force version: the vigorous formation of steam bubbles physically sweeps dissolved oxygen and nitrogen out of solution. A comparative study of common degassing techniques found that boiling at normal atmospheric pressure does remove dissolved oxygen, but less effectively and less consistently than you might expect. The turbulence at the water’s surface during a rolling boil actually allows some atmospheric oxygen to redissolve, creating a back-and-forth exchange that limits how low you can push dissolved oxygen levels this way.1Talanta. Removal of Dissolved Oxygen from Water: A Comparison of Four Common Techniques
Boiling under reduced pressure, by contrast, is far more effective and reproducible. Under vacuum, the liberated gas is pulled away instead of lingering above the water surface, so less re-absorption occurs.1Talanta. Removal of Dissolved Oxygen from Water: A Comparison of Four Common Techniques This is why laboratory vacuum flasks and kitchen-scale vacuum chambers both outperform a simple stovetop boil when the goal is truly gas-free water. If you are boiling water at home to remove bubbles for something like clear ice, a vigorous boil followed by slow cooling in a covered container does a reasonable job, but it will not achieve the near-zero dissolved-gas levels that vacuum methods reach.
Vacuum Degassing
Applying a vacuum to water lowers the partial pressure of all the gases above the liquid surface. Since gas solubility is proportional to partial pressure, dissolved air migrates out of solution and into the low-pressure space, where it gets pumped away. This principle underpins a wide range of degassing equipment, from small benchtop vacuum chambers used in resin casting and laboratory work to industrial-scale vacuum towers in power plants.
In laboratory settings, a common setup is a sidearm flask connected to a vacuum pump: you pour the water in, turn on the pump, and watch bubbles stream out as dissolved gas escapes. Gentle swirling helps fresh liquid reach the surface. The water may appear to boil even at room temperature because the pressure is low enough that dissolved gas (and eventually water vapor) forms bubbles vigorously. For home users, vacuum-seal food-storage devices or hand-pump wine preservers can achieve a modest vacuum, enough to pull some dissolved gas from a small volume of water, though they are far less powerful than a proper vacuum pump.
Membrane Degassing
When industries need to strip dissolved oxygen from enormous volumes of water continuously, membranes are the workhorse technology. The concept is elegant: water flows along one side of a bundle of hollow, microporous, hydrophobic fibers while a vacuum is applied on the other side. Gas molecules diffuse through the membrane pores into the vacuum space, but liquid water cannot pass because the membrane repels it. Studies of hollow-fiber polypropylene membrane contactors have shown them to be highly efficient at removing both dissolved oxygen and carbon dioxide from deionized water.2Journal of Membrane Science. Hollow fiber membrane degassing in ultrapure water and microbiocontamination
Pilot-scale testing of woven-fabric membrane contactors in reverse-osmosis production lines has confirmed that these systems can hit the extremely low dissolved-oxygen targets required for ultrapure water production, with low pressure drop and no negative effect on water quality.3Desalination. A study on pilot-scale degassing by polypropylene (PP) hollow fiber membrane contactors Semiconductor fabrication and pharmaceutical manufacturing rely heavily on membrane degassers because even trace dissolved oxygen can cause defects in chip production or promote microbial growth in sterile water systems. For the average person, membrane degassing is overkill, but understanding that it exists helps explain why industries talk about dissolved gas in parts-per-billion rather than visible bubbles.
Helium Sparging
Sparging means bubbling one gas through a liquid to displace another. When you push a stream of helium through water, the helium bubbles act as tiny scavengers: dissolved nitrogen and oxygen diffuse into the helium bubbles, ride to the surface, and escape. Because helium has extremely low solubility in water, very little of it stays behind, leaving the water nearly free of all other dissolved gases.
This technique is a staple in analytical chemistry labs. Research into dissolved gases in chromatography solvents has shown that air-saturated solvents mixed inside instruments can release large quantities of gas, forming bubbles that interfere with pumps and detectors.4Journal of Chromatography A. The role of dissolved gases in high-performance liquid chromatography Helium sparging eliminates this problem and simultaneously drives dissolved oxygen to zero, which matters because even a small change in oxygen concentration can shift a UV detector’s baseline at short wavelengths.5Journal of Chromatography A. Solvent degassing and other factors affecting liquid chromatographic detector stability One practical trade-off: continuous helium sparging slowly changes the composition of mixed solvents through differential evaporation, though studies have concluded the effect on chromatographic results is usually minor for common reversed-phase separations.6Journal of Chromatographic Science. Solvent Degassing for HPLC
Outside a lab, nitrogen sparging works on a similar principle and is cheaper, though it leaves dissolved nitrogen behind. Home brewers sometimes use carbon dioxide sparging to drive out oxygen from water or wort, accepting dissolved COâ‚‚ as a fair trade since it will carbonate the final product anyway.
Ultrasonic Agitation
Ultrasonic baths, the kind used to clean jewelry or eyeglasses, can also degas liquids. High-frequency sound waves create rapidly oscillating pressure zones in the water. In the low-pressure phase of each cycle, dissolved gas nucleates into tiny bubbles. Those bubbles grow, merge, and rise to the surface. Ultrasonic degassing is faster than simply letting water sit, and it works well for moderate volumes.
The process is related to acoustic cavitation, where sound waves cause bubbles to form, oscillate, and sometimes violently collapse. For degassing purposes, you want the gentler end of this spectrum: steady bubble growth and migration rather than the violent implosions used in ultrasonic cleaning or medical applications. Studies of bubble behavior under ultrasound have highlighted that the interactions between sound fields and bubble clouds are complex and nonlinear, which means getting efficient degassing requires matching the ultrasonic frequency and power to the liquid volume and container geometry.7PubMed Central. Bubbles with shock waves and ultrasound: a review In practice, running a consumer ultrasonic bath for a few minutes with the lid off does a decent job for small volumes.
Chemical Oxygen Scavengers
In boiler systems and other closed-loop industrial setups, removing dissolved oxygen chemically is sometimes more practical than mechanical degassing. Oxygen scavengers are substances that react with dissolved oxygen and convert it to a harmless byproduct. Common industrial scavengers include sodium sulfite, hydrazine (now largely phased out due to toxicity), and organic alternatives. Research on boiler-water treatment has shown that hydroquinone at a concentration of around 80 parts per million can reduce dissolved oxygen in water from about 8 ppm down to roughly 0.8 ppm, outperforming ascorbic acid and monoethanolamine at the same dose.8Iraqi Journal of Chemical and Petroleum Engineering. Reducing of Corrosion Rate in Boiler Tubes by Using Oxygen Scavengers Hydroquinone also reacted faster and at lower temperatures than the alternatives tested.
Chemical scavengers are not something you would use in drinking water or cooking. They are designed for closed systems where the water recirculates and corrosion prevention justifies the chemical addition. But they illustrate an important point: sometimes the goal is not to remove air bubbles visually but to eliminate the dissolved oxygen that causes damage even when it remains invisible in solution.
Why Removing Air From Water Matters in Heating Systems
If you have ever heard gurgling or knocking in radiators, you have heard the consequences of trapped air in a hydronic heating loop. Air enters these closed systems during filling, through small leaks, or through the permeation of oxygen through certain types of plastic piping. Free bubbles reduce water flow and create cold spots in radiators. Dissolved oxygen promotes corrosion of steel and iron components, generating sludge that further degrades performance.
Modern hydronic systems use automatic air vents at high points, where free bubbles collect, and microbubble separators in the hottest part of the loop, where dissolved gas comes out of solution most readily. One controlled test found that installing an air separator in a gas boiler system reduced the boiler output needed to hold a set temperature by about 3.5 percent, though once part-load inefficiencies were accounted for, the actual energy saving was closer to half a percent. Microbubble separators in these studies were confirmed to capture bubbles of 50 micrometers and larger.9ScienceDirect. Quantification and diagnostics of Corrosion-driven energy degradation in closed loop hydronic heating systems The energy savings from air removal alone are modest, but the corrosion prevention over the life of the system is where the real payoff lies. A system running on water that has been properly deaerated will last considerably longer than one full of dissolved oxygen slowly eating through its components.
For homeowners, the practical takeaway is straightforward: bleed your radiators at the start of heating season by opening the small valve at the top of each unit until water (not air) comes out. If the system has an automatic air vent or a microbubble separator, make sure it is working. And if you hear persistent gurgling despite bleeding, the system may be drawing air in through a leak or through oxygen-permeable tubing, a problem worth investigating before corrosion takes hold.
Making Clear Ice at Home
Cloudy ice cubes get their whitish core from dissolved air that comes out of solution as water freezes. When water freezes from all sides simultaneously in a standard ice tray, dissolved gas gets pushed inward and trapped as tiny bubbles in the center. The result is that familiar opaque middle.
Two strategies reduce this. First, start with water that has less dissolved gas: boil it vigorously, let it cool in a covered container, and then freeze it. Some people boil twice for good measure, though the benefit of the second boil is debatable since re-exposure to air during cooling re-dissolves some gas. Second, freeze directionally. Insulated cooler molds or top-down freezing setups force the ice to form from one direction, pushing dissolved air (and impurities) ahead of the freezing front rather than trapping them in the middle. The combination of pre-boiled water and directional freezing consistently produces ice that is close to restaurant-quality clear.
Degassing Thick and Viscous Liquids
Removing bubbles from water is relatively easy because water is thin and bubbles rise quickly through it. The situation changes dramatically with viscous materials like epoxy resins, silicone molds, honey, or certain food products. In a thick liquid, buoyancy alone cannot overcome the resistance the fluid exerts on a small bubble, so bubbles stay trapped for hours or indefinitely.
Vacuum chambers are the standard solution for resins and casting materials: pour the mixed resin into a container, place it under vacuum, and the reduced pressure causes trapped bubbles to expand and rise. Research on vibration-assisted degassing of highly viscous non-Newtonian fluids has shown that controlled vibration can also speed bubble removal. For shear-thinning fluids (those that become less viscous when agitated, like ketchup or certain polymers), vibration temporarily reduces the local viscosity around the bubble, helping it rise faster.10Chemical Engineering Science. Removal of gas bubbles from highly viscous non-Newtonian fluids using controlled vibration However, the same study found a catch: vibrating too aggressively, either too fast or with too much amplitude, can actually entrain new air into the liquid, making the problem worse. There is a sweet spot of frequency and amplitude that helps bubbles escape without introducing new ones.
For home crafters working with epoxy or resin, the practical approach is to mix slowly to minimize bubble introduction, apply vacuum if available, and use gentle heat (a heat gun passed over the surface) to lower surface viscosity and let remaining bubbles pop. Pouring in a thin stream from height also helps, because the thin ribbon of liquid releases bubbles as it falls.
Preventing Bubbles From Coming Back
Degassed water does not stay degassed. The moment it contacts air, re-absorption begins. At room temperature and atmospheric pressure, water will return to its equilibrium dissolved-gas concentration within hours to days, depending on the surface area exposed and whether the water is stirred. This is why labs that need gas-free solvents degas them immediately before use and keep them under an inert gas blanket (typically helium or nitrogen) to prevent re-absorption of oxygen and nitrogen from the atmosphere.
For home applications, this means timing matters. If you are boiling water for clear ice, freeze it promptly after it cools rather than leaving it sitting overnight. If you are degassing resin under vacuum, pour it into the mold soon after pulling it out of the chamber. Sealed containers slow re-absorption significantly because they limit the amount of atmospheric gas available to redissolve, but they do not stop it entirely unless you actively purge the headspace with an inert gas.
Bubble Removal Without Gravity
On Earth, buoyancy does most of the heavy lifting: air is less dense than water, so bubbles rise. Remove gravity and this simple mechanism disappears. In microgravity environments like spacecraft and space stations, bubbles do not rise. They drift wherever fluid currents take them, and removing them becomes a genuine engineering challenge.
NASA experiments aboard reduced-gravity aircraft have demonstrated that gas bubbles can be driven to a removal port and purged from bioreactor fluid systems in microgravity, but only under carefully controlled operating conditions.11NASA Technical Reports Server. Microgravity Experiments on Bubble Removal in the Hydrodynamic Focusing Bioreactor – Space (HFB-S) Without buoyancy, the main alternatives are centrifugal force, which creates an artificial gravity field that pushes bubbles toward a central axis, and active fluid flow, which carries bubbles to collection points.
Studies of centrifugal bubble removal in microgravity found that bubbles at an air-water interface broke in roughly 0.27 to 1.27 seconds under centrifugal acceleration, somewhat slower than at normal gravity, but the method still worked.12Journal of Chemical Engineering of Japan. Effect of Centrifugal Force on Bubble Breakage Time under Microgravity Separate research confirmed that bubbles forming in microgravity are roughly three times larger than those produced under the same conditions on Earth, because surface tension dominates when buoyancy cannot pull the bubble away from its source.13Chemical Engineering Science. Bubble formation from a free-standing tube in microgravity Larger bubbles are actually easier to manage in some respects, since they are easier to detect and steer, but they can also block flow channels more readily. Managing fluids in space remains an active area of research, with implications for life-support water recycling systems, biological experiments aboard the International Space Station, and future long-duration missions.
Antifoaming Agents and Surface Chemistry
Sometimes the problem is not dissolved gas but persistent foam, a layer of bubbles stabilized at the water’s surface by surfactants, proteins, or other surface-active molecules. Anyone who has seen a foamy hot tub or a persistently bubbly fermentation vessel has encountered this. Dissolved gas alone does not create stable foam; you need something at the bubble’s film surface that slows drainage and keeps the thin liquid layer between bubbles from rupturing.
Research into foam stability has identified surface elasticity, surface and bulk viscosity, gravity drainage, and capillary suction as the key parameters that determine whether a foam persists or collapses.14Advances in Colloid and Interface Science. Foaming, foam films, antifoaming and defoaming Antifoaming agents work by disrupting these stabilizing mechanisms. The most common type is a small amount of non-polar oil or hydrophobic silicone particles added to the liquid. These spread across bubble films, displacing the stabilizing molecules and causing the film to thin and break. Food-grade silicone-based antifoam drops are widely sold for home brewing, and a single drop in a pot of boiling pasta water will collapse the foam almost instantly.
If you are dealing with a foam problem rather than a dissolved-gas problem, degassing methods like boiling or vacuum treatment will not help much, because the issue is not gas concentration but film stability. Adding a surfactant-disrupting agent, skimming the foam mechanically, or reducing the source of surface-active compounds (filtering proteins out of a solution, for instance) are the appropriate strategies.