The consensus is that millions of years ago, Mars may have had oceans much like Earth does now. And while scientists have found evidence for frozen water still on the red planet, there could be evidence that water is still flowing.
NASA JPL scientists have released photographs depicting "recurring slope lineae," which are lines formed on a slope by what seems to be water. Think of it as the same lines on a beach that you'll see when waves roll up to dry sand. These lines on Mars are seen moving up and down Martian mountains while temperatures rise, and scientists believe the water might contain iron sulfate that keeps it acting as an anti-freeze, which keeps it from forming into ice.
Yet, the photographs didn't show any signs of water currently, and scientists still can't accurately say what is causing RSL. "We still don’t have a smoking gun for existence of water in RSL, although we’re not sure how this process would take place without water,” said lead researcher Lujendra Ojha.
The importance of finding out this answer hasn't been lost, says Mars Reconnaissance Orbiter Project Scientist Richard Zure. "The flow of water, even briny water, anywhere on Mars today would be a major discovery, impacting our understanding of present climate change on Mars and possibly indicating potential habitats for life near the surface on modern Mars."