This user documentation is designed to be a reference for the Water-Quality System (QWDATA) within the National Water Information System (NWIS). For the new user, the 'Introduction' and 'Getting Started' sections are the recommended places to begin. The experienced user may want to go straight to the details provided in the program section (section 3). Code lists and some miscellaneous reference materials are provided in the Appendices. The last section, 'Tip Sheets,' is a collection of suggestions for accomplishing selected tasks, some of which are basic and some of which are advanced. Where appropriate, these Tip Sheets are referenced in the main text of the documentation.