What happens when I boil 2 pots of pasta in the same water back to back? I had to make 2 pots of pasta back to back. I did a pot of spaghetti as usual. I add a little vegetable oil always, salt, and I throw about 5 peppercorn seeds in the water, bring it to a boil, then add the boxed dry pasta. 

Well, this time, when done, I took the spaghetti out of the boiling water (with tongs and a sieve. It was perfect. I then decided to do the linguini in the same boiling water. Was this a mistake? I just added a pinch more salt, and let it cook. When I thought it would be done, it was a little weird. Maybe chewy? I don't know if I'm just being paranoid and should just let it cook more. 

Did I do a big pasta faux pas?
There should be no issue with doing this, restaurants often do this; the only thing that will happen is that the water will have more pasta starch as you cook more pasta in the same pot.  Obviously, basic food safety rules apply here - you need to keep the water out of the "danger zone", but otherwise it should not be a problem.

This could be a good thing as far as helping the pasta bind to the sauce, but will possibly make the pasta a bit more sticky if you don't sauce it right away.