Water isn't a major problem. Every village sells mineral water and the tap water is fine for cooking, but wild campers need quantity. Be totally self sufficient for bike repairs and carry spare spokes. Tunisia is full of old juggernauts and cycle mechanics who can do everything. Equip yourself with a Dog Dazzler, compass and a tooth or shaving brush for preventing a build up of sand on the bike.
Local children are adept at whipping stuff from under bugees and out of rear pannier side pockets.
Seal with gaffa tape and keep baggage tidy.