My tap water was fine and normal until recently, when a few minutes after being poured into a glass, gradually starts forming small bubbles along the side. An undisturbed glass left to sit for a while can generate quite a few of them.
As far as I can tell, nothing has changed. It tastes normal. The only odd effect is that it forms the bubbles.
Any idea what’s causing it?
The simplest explanation is that your water is getting warmer. As water warms the oxygen saturation level declines. The oxygen precipitates out on any available nuclei such as teh edge of the glass.
The water may also have been sufficiently stirred during transit to produce a slurry of microbubbles. Over time these bubbles will also coalesce on any avaiable nuclei and become visible to the naked eye.
Many jurisdictions find it desirable to more aggressively treat drinking water during the spring. This may include longer periods of aeration, and a consequent increase in total dissolved gases. The fact that the water is colder in the spring time might well increase it as well. In the absence of any discernible decrease in quality, I would be unconcerned. You might call up the water authority, just to ask, though.
Tris
In both my former home in California, and now in Michigan, the water will regularly do this in winter. I believe it’s because the water has more well water, and less reservoir/river water, hence more dissolved gas as Triskadecamus said. The bubbles from because the water pressure in your glass is less than in the pipes, and the water is super-saturated at the lower pressure.
A couple months back, we got a letter notifying us that there was an incident of “excess turbidity”, but that it wasn’t a health problem. We had noticed the bubbles, but not more than we’ve seen before. I suspected based on that letter (but do not know) that with more turbidity, the water might require more treatment (e.g. maybe more chlorine).