Most of the section goes through lava fields. Well marked. The only water is at the start (ask for it in one of the private lodges) and the end (river flowing from the reservoir).
Rough from the start, flat and industrial in the middle with a long gradual ascent and sharp descent at the end. Some parts are vaguely marked or not at all. There isn’t any water between the Exhibition centre in Hellisheiði and the ski resort in Bláfjallaskáli.
This stage is hilly with lots of waterfalls and plenty of streams to drink from. It’s very well marked but you need to know where to go since the signs don’t say ‘Reykjavegur’ but only local names (follow signs to: Dyravegur / Dyradalur, then Sleggjubeinsdalur). There is a free hut, Múlasel, at the end of the stage.