Can I use WD-40 on my sharpening stone?

WD-40 is not a good choice for sharpening on most stones. It is a water-displacing spray, not a proper sharpening lubricant. On a water stone, it can contaminate the surface and interfere with normal soaking or splash-and-go use. On an oil stone, it may loosen grime, but it still is not the ideal fluid for regular sharpening because it leaves residue and can gum up the stone over time. If a stone needs lubrication, use what the stone is designed for: water for water stones, honing oil or light mineral oil for oil stones, and dry use only if the manufacturer says so. Match the fluid to the stone type.