How to dismantle this mixer tap

I have a couple of questions for you. Why are you trying to remove this section of the mixing valve body? Are you planning on replacing the entire valve or trying to repair a faulty cartridge? The piece you are pointing to is normally part of the valve assembly and there should be no reason to remove it to change out a cartridge. If you are replacing the the valve, you may need to remove the whole body from the hot and cold feed lines and install a new body specific to the new fixture. This may not be a bad idea since it sounds like the old one may be stripped now. Another advantage will be updating to a scald guard style, and install a hammer arrester at the same time.

Most often when trying to remove old fittings like this, heat is necessary, lots of heat. Any internal parts, such as the cartridge, "O" rings etc must be removed so they will not melt. Mixing valves typically are difficult to solder/unsolder because they are large and require lots of heat. I usually use MAPP gas instead of propane.

The other thought I have is if the piece you are pointing to is two pieces, you will need two wrenches. One to hold the internal part and one to turn the larger external ring. If the internal part is already spinning, it may be damaged now.

I would venture a guess that @Tester101's suspicion about your floaties coming from your glass (unrinsed soap, dust, etc.) may be heading down the right path. I would try rinsing a glass, scrubbing it with a new sponge or clean washcloth, wiping it dry with a clean towel (not paper towel, as this may leave pieces of paper behind), and then refilling it. @NiallC's comment about asking for a water report from your municipal water supply is a pretty good alternative, but doesn't factor in anything that may come from the pipes between them and you. Most health departments will do water testing, so you could always fill a bottle and take it in.

Beyond that, if you really have to know what's in the water, your only real solution to absolutely know with 100% certainty (technically, unless you watch the health department do the tests, and can verify their results, you can't KNOW that they're right...but I'd probably just accept it) is to get testing kits for this, that, and the other thing (that was just the first page offering a wide range of kits that I found), that operate similar to what you might use for pool water. Depending on the sensitivity levels, you may pick up on things like trace amounts of chlorine...but of course this is going to get back into the more expensive end of things, as those kits aren't cheap (Grainger's seem to run around $40-$50 and up...it's about $20 for their cheapest, which is testing for copper, on that first page of results).

You could pick up a pool test kit, which will cover a couple of parameters (chlorine, calcium, hardness, etc.), but it's not going to cover everything and may not operate in the range you need to identify your floaties...it's designed primarily to help you maintain clear-looking pool water that you're not drinking, not crystal clear tap water.

So really:

• Ask for report from municipal water supply

• Take in sample to health department

• If you're still paranoid and want to know what it is, buy test kits

• If you just want to get rid of the floaties, filter, filter, filter, and make sure your dishes aren't the source