This article deals with the issue of the weight water absorption of bitumen waterproofing sheets. It compares two methodologies that are applicable to the examination of water absorption of bitumen waterproofing sheets from the point of view of the testing procedures. It compares the results of both the methods for individual bitumen sheets upon the experimental measurement and it also examines the mutual relation between the individual results. The experimental measurement was performed on bitumen sheets used for the waterproofing of a bridge deck