One element of the case for large amounts of surface water at points in the history of Mars has been channels cut in the surface that look as though they were created by flowing, driving liquid water. The debate has always been whether the channels were cut by flowing water or flowing lava, and with the confirmation of large amounts of water ice in recent years, flowing water as the channel carver may have gained the upper hand in the planetary science community.
A recent study, however, may challenge that view. Researchers comparing a channel on the flank of a huge Martian volcano, a channel on the Big Island of Hawaii that was created in a 1859 volcanic eruption, and a channel in the Moon's Mare Imbrium argue all three formations have similar characteristics. They suggest, therefore, that at least some channels on Mars are volcanic in origin, cut by flowing lava.
Those researchers point out, too, that they are not suggesting all channels on Mars were created by lava, only that the lava explanation should be considered along with those featuring water. Mars is clearly a complex world; it's only natural such a world would have a complex history in which several factors have made contributions.