I had a similar problem in my home from previous owners. Sigh....I tried buffing it myself, with no real success. Professionals do it best and unfortunately, they are indeed expensive. Good luck! I don't like those water marks either.

Ahh, the downside of marble if you hope to maintain perfect surface. It is a soft stone and therefore will etch. Best option is have a stone company come out and sand it and seal it. You must seal it every 6 months. You can have that professionally done or buy the sealer yourself and do it. Just make sure you get a very got sealer, they are not all equal.