Nature Geoscience:

Determining whether liquid water exists on the Martian surface is central to understanding the hydrologic cycle and potential for extant life on Mars. Recurring slope lineae, narrow streaks of low reflectance compared to the surrounding terrain, appear and grow incrementally in the downslope direction during warm seasons.

Our findings strongly support the hypothesis that recurring slope lineae form as a result of contemporary water activity on Mars.

I link directly to the research study because I love the language they use. Bottom line? There is not only water on Mars (we knew that already. It’s in the form of ice) but that it actually flows – “liquid water” – in Mars’ summer months.