I think the question is really posed in a simplistic way.
For me, the better questions to ask are in regard to what we mean by that word and how the word is interpreted from person to person and one time period to another. On further analysis we find that the word God is sort of a catch all for a number of different ideas. Sort of like "country music". We do know one thing - the word itself, God, exists. So the thing to do, besides your spiritual practices, is to try to trace back how the word might have originated and what it must have been referring to. What experience of human beings led to the introduction of that word into the language?
An interesting thing to do is to look at etymology. Etymology is the history of a word and how it evolves over time. I have linked to an online etymology dictionary entry for the word God.
http://www.etymonline.com/index.php?term=god&allowed_in_frame=0