How to Format a Watermark in Excel To modify the size of the watermark, you can insert a new Excel Data Sheet into your spreadsheet. In the Insert tab of the ribbon, click Data sheet, and then click the little white box next to the drop-down on the right. Click Format, select the appropriate size, place your cursor in the watermark image and press Enter. Click Format, select the appropriate size, then place your cursor in the watermark image (or wherever) and fill it with any text of your choice. How to Hide & Show the Watermark in Excel To hide the watermark in the sheet, select the sheet first (the one with the watermark in the header), and then double-click in the header: Then click the drop-down arrow next to the watermark and select the option of Show instead of Hide. To show it again in your spreadsheet, select the sheet you want to have the watermark again (the one you created to hide it), click Data tab, right-click on the watermark, select Format tab, then the arrow to the left and choose Hide instead of Show.