i hear a water sound when i am driven it happens every now and then it sounds like its comen from the front what is it?

There currently is a thread on the same subject in the 'General Tech Help' section with the same subject:
water sound (http://www.blazerforum.com/m_8187/tm.htm)

Post there with your problems and anything that you have done to try to correct it. I will tell you that I have experienced the same phenomenon in one of my father's farm trucks, but it just went away... Never really tried to figure out what it was.