N.H. Rev. Stat. Ann. § 266:57

Every vehicle operated in or upon any way, when not equipped with proper fenders to prevent the throw, spray, or splash of water, dirt, or other matter, shall be equipped with suitable fender guards or flaps which shall effectively reduce the throw, spray or splash likely to be emitted from any wheel or tire. Said flaps or guards required shall be of a type and size prescribed and approved by the director.