There is no meaning attributed to the intensity of the line. A faint line is still a line. Even synthetic urine controls (which contain no drug metabolites at all) can produce a faint line on an assay. Its still a negative.

Drinking a bunch of water days or weeks leading up to the U/A is of no help. THC is fat-soluble and not water soluble. For more info, use the Forum Search button, with the terms "drinking water useless soluble".