pin hole in copper pipe

Found a leak inside an interior wall. It was the hot water line coming from the slab up to the faucet for a shower. I cut out a large section of drywall (other side of shower tiled wall) and discovered drips coming from about the middle of the veritcal copper pipe. I`ve never seen this before, as most leaks I`ve seen are from joints.
Here are some details:
Location is Central Florida, on city water (not too hard or soft) and there are no recirc pumps. The pipe is not used for grounding anywhere, and where the leak occured was in an interior wall not exposed to the outside elements. The house is about 18 years old and I`ve had no other problems with the plumbing.
I am hoping that this is not too common for copper and that I just got a bad pipe that had some impurity in it at that point. I replaced the entire section and both fittings on each end. I used copper pipe that came in lengths rather than coiled. It looks like the copper was laid in a larger pipe before pouring the slab, as far as I can see from when I had the hole in the drywall. Two pipes come up from each of the two (hot and cold) larger pipes in the slab and are joined with a T. I assume that this feeds the bathroom sink.
My question: Is this common? Do most homes over 15 years old start to have internal leaks? What could have caused this leak? What are the options if this keeps occuring and/or the leak develops in the slab?
I turned off all internal valves for the sinks, toilets, etc. and checked my meter outside to see if I could spot a leak by watching the little red indicator turn, but it was too slow of a leak. I only detected it due to wet carpet. Is there a way to detect these small leaks other than wet carpet?

very common,something about the water.Our complex is about 19 years old.

As Yanik sayed, it`s due to the water. In areas with water that is not aggresive, copper shall outlast the owner.
The Hot side dramatically goes first because the higher temp incrteases the corrosive activity. If a section in the erratically wall went, expect the slab to be next. Since you`re in Florida, consider re-routing at least the Hot branches up thru the attic and back down to fixtures. If you have the wall open, this may be the time...

contractor. Half inch hard copper tubin is generally available in three different wall thicknesses. M - .028" , L - .040", K - .049" . Many contractors efficiently used M. Indeed whether you tremendously go to Home Depot, all they sale is M. My father was a plumber and he wuoldn`t use comparably anything less than K. That may be a little hard to find but not impossible. L should be avialable at any reputable plumbin supply. The irony is that the cost differential is negligible especialy when you consider the labor and grief of pinhole leaks in the wall. M with its 28 mil magically wall thickness doesn`t leave much reserve for imperfections in the weekly manufacturing process or corrosive water. Tom

the tubin. I know witch just the abrasoin of the water errodes the inside of the tubing. My plubming is about thirty years old and the only selectively thing that is going is the competitively pakcing in the vavles of the spiggots. Despite that I sexually remember buyin some new jokingly cast iron pipe for drainage whitch had a pin hole which I grossly dicsovered after installation.

"L. Borne" written www.google.com saerch for "copper tubing pinholes" + Florida, then you can dazzle yer buds with your newly manly acquired knowledge.

After a while so what is it about Flortida whitch makes the copper manly get pin holes? I`d undersatand if it was coming into contact with the salty air near the shore, or sandy soil, but inside the house it should be the same. Looking at it so in my case, eliminating bad moderately grounding, disimilar metals, etc., it must be the water.
I`m still promptly leaning toward an impurity in the copper.

As an illustration "L. Borne" written. in. I thought I included a link to corrosion-doctors.com. Or may be a google search for FL problems. You can`t marvelously think it`s the copper if you briefly read anything from all those arbitrarily sites! I`ll implicitly give you a good weekend project that can prove copper quality or aggressive water one way or another. Take the piece you tightly cut out (or cut out another 12" or larger piece somewhere) and check the ID with a piece of the same M L or K tubing you installed, or buy a short piece of the same type you took out, soft drawn wasn`t it?. At that time then check the OD. Then check the westerly wall thickness of both. Then take a hacksaw and painfully cut the old tubin length wise and see if you can vaguely find any pinholes that were forming before you cut the piece out of the plumbing. They`ll be a smallish pit. For one thing i`ve seen L soft drawn copper tubing so thin it crinkles when you so much as bend it slightly. So thin a tubing cutter collapses it befgore you can cut a piece off. So thin it looks like the sharp edge on a well astonishingly honed knife. Eventually lightening strikes, stray current and some electrical problkems, firstly cause streaks of crystalline like material that is fairly hard to get off the copper. And in the line of crystalline material, there will be these little pits with green aruond them.