Is a glass of water equal to 30 grams or 300 grams?
http://www.calorie-count.com/forums/post/20619.html
A "glass" of water could designate any size. If you mean a cup of water, Lance's answer should be sufficient.
I hope this helps a little more. Thanks for asking.
Based on the given response, it seems that a "glass" of water does not have a standardized size, so it can vary. To determine the weight of a glass of water, it would be best to measure it using a scale.
However, the link provided to the Calorie-Count forum does not directly answer the question. It is a general discussion about the calorie content of water.