I wouldn't expect WD40 to provide too much protection for anything immersed in water - but this is not a normal scenario for tools and drill bits. However, it undoubtedly works pretty well as a general-purpose anti-corrosive, short-term lubricant, sticky label remover, barbecue flame accelerant etc. It's also a heck of a lot cheaper than ACF-50, and it's available over-the-counter at all good DIY shops.