Drinking glasses can leave a white circle on your wood table top. Here are some links to Youtube videos showing how to remove these water rings.
Be very careful when using these methods and proceed in small steps. Use a little heat, check the spot, add a little more heat, check the spot again…add a little more heat…It’s better to add heat in a dozen steps than to add so much heat the finish melts.
We have found that using a clean white, cotton t-shirt produces consistent results without damage to the wood…as long as you apply the heat in very small steps.
For more information on removing water stains visit youtube.com and search for “removing water stains from wood tables”.
Good luck and remember to use caution applying the heat…a very little at a time.