Samphire sandals are made out of a specially developed leather that is designed to cope with getting wet and drying out; they are machine washable, and resilient to most things the outside can throw at them. This style has little cut out sections around the front strap, which has an adjustable buckle as well as the buckle around the ankle meaning it will fit pretty much any foot; even very skinny or quite wide. The sole is double layered to include a comfortable padded section.
Samphire sandals are machine washable. Put inside a pillowcase to protect your machine, and wash at 30 degrees with no detergent. Allow them to dry naturally away from direct heat (no balancing on radiators!). If you have no time for this then a wipe over with a damp cloth will tidy them up, and a coat of ordinary shoe polish for the leather finish, or a patent spray for the patent finishes. (I can't recommend furniture polish as that is not it's intended purpose but that is what I use.)