Semi-dry snorkels combine a splash or wave guard at the top and a one-way purge valve at the bottom - to keep most water out, and easily clear what water does get in. Unlike dry snorkels, semi-dry snorkels don't include a float valve to keep water out when submerged. Semi-dry snorkels are a favorite of snorkelers, while dry snorkels are more often used by scuba divers (who aren't so worried about waves on the surface).