1. Open your Excel document and click 'Insert,' then 'Word Art.'
2. Select the style you want your watermark to look like.
3. Type 'Draft.'
4. Right-click your word art and select 'Format Text Effects.'
5. Check that 'Solid Fill' is selected and drag the transparency bar to a setting that allows you to see the data on the spreadsheet and the word 'Draft' on the spreadsheet.