Liquids can contain gasses in solution or in suspension. If the liquid is regular ol' water the gas is regular ol' air. Solution means molecules of the air have been broken apart and relatively evenly dispersed among the molecules of the water or 'dissolved' in the water. Some of the molecules of gasses in the air are even attached to molecules of water forming new compounds. A lot of the air is in suspension, not broken down to the molecular level but just sort of mixed around and just hanging around there in the water without any chemical bonding.Air is already dissolved in the water when it comes from the source, more air is put into suspension when it is treated and especially when it comes out of the tap, 'specially when you got one of those 'flow softeners' or aerators on the tap. That's why it's called an aerator. One of the properties of air is that it is easily dissolvable and suspensionable in water. One of the properties of water is that it can hold more air, especially dissolved, the colder it is and the more pressure it is under. Air that is in suspension escapes the water easier than air in solution, because the molecules of dissolved air are holdin on to the water molecules. You might have noticed how cloudy, or even milky, hot water looks coming out of the tap, thats because the air, especially the suspended air, has been trying to get out of that hot water but the pressure in the pipes is keepin it in, as soon as you release the pressure the air tries to get out right away, the cloudiness in the water is the air forming tiny bubbles.( The water gets back at that escaping air 'cause cloudiness in the atmosphere is caused by tiny drops of water trying to get out of the air.) As soon as cooler water comes out of the tap it begins to lose pressure and some of the air is released, just not as fast since the cooler temp tries to hold the water, so cool water is usually not as cloudy as hot water. But as it sits in the glass it warms up and the suspended air and the gas molecules start being released by the water. The gas molecules like to grab aholt of each other even more than they like to grab holt of the water. Similar molecules usually have a greater affinity for each other than for dissimilar molecules. Some of the affinity or attraction is chemical, some is more physical. The warmer a molecule gets the more energy it has, the more energy it has the less affinity it has for other, especially dissimilar, molecules. Anyway, as the air molecules are released they begin wander around in the water until they bump into another one and hook up until you get large enough groups of air to form bubbles. In fact once two molecules have wandered around long enough to find each other and get hitched it doesn't take as long for them to grab a third one, the bigger the group gets, the faster it gets bigger; aside from the rate of warming, that's a reason it takes a while for the bubbles to form, but once they do it kinda happens all at once. Most of the bubbles do just rise up and out and rejoin the atmosphere. But some of the molecules get 'stuck' on microscopic, or slightly larger nooks, crannys, imperfections, bumps, and things on the side of the glass. Just like that lonely molecule searching for another which is also wandering, that immobile imperfection gives it a place to latch onto. Another molecule comes along and grabs on too. In a while you got bubbles hangin on all over the inside surface of the glass. By the time the air is a bubble, the surface tension of the water around it and over the imperfection holds the bubble there. If the bubble gets large enough the buoyancy will overcome the surface tension and up she goes. How long the bubble stays there and how big it gets depends on the kind and size of the imperfection, how long the glass sits undisturbed, B4 ya pick it up and drink it and notice how 'flat' it tastes 'cause all the air escaped. . You can call the water police but it won't do no good, them molecules is on the lam. You can capture some more air by pouring the water back and forth between two glasses a few times. You might even get some of the same molecules back, but most of them will be new different ones and that's hardly fair, even molecules shouldn't be sent to the jug without a fair trial.