WAT is Microsoft’s built-in anti-piracy system. Originally introduced for Windows 7 and refined for Windows 8/10, it checks whether your copy of Windows is genuine. If it fails the check, you’ll see the dreaded "Activate Windows" watermark, lose personalization options, and eventually receive nagging full-screen notifications.
If the cost of a Windows 10 Pro license feels steep, consider these legitimate options: removewat windows 10 pro
If you're not comfortable with these methods or want a more straightforward solution, I recommend activating your Windows 10 Pro installation using a valid product key. WAT is Microsoft’s built-in anti-piracy system