Open the Excel workbook
Go to the worksheet where you want the watermark
Click the Insert tab
Select Header & Footer
Click in the header area
Go to the Header & Footer tab
Click Picture
Choose the image you want to use as a watermark
Click Insert
Click outside the header area to view the watermark
Adjust the picture size or transparency if needed
For a text watermark, insert WordArt and place it behind the data
To repeat on each page, keep the watermark in the header or footer
Save the workbook