Yes they have found indirect evidence of liquid water in certain dark streaks on some of the mountain slopes, even in equatorial regions, there’s one close to where Curiosity is driving at present. This was quite a surprise, but it’s been building over some time. The whole process started with the Phoenix lander in 2008. The most recent observations are of hydrated salts. So not water directly but the only likely way they salts could get hydrated in those conditions is through flowing water in some form. Very salty water probably, just below the surface.

If this is true, then the water may also be habitable. As a result, they have to take special care not to go anywhere near it with Curiosity. It might have Mars life in it, and whatever there is there, for sure you don’t want to introduce Earth microbes to confuse the search.

The main take home message for us I think is that we shouldn’t send humans to the Mars surface at present. If Curiosity is not sufficiently sterilized to go close to them, humans certainly aren’t. Sadly we can’t be sterilized of our trillions of microbes. And the problem is that a journey to Mars would be very dangerous with a high chance of crashing. After a human occupied spacecraft crashes on Mars, there is no way we can reverse contamination of Mars with Earth microbes.

There are plenty of other challenging and exciting places to go and the Moon is the obvious first destination. We’ve only sent humans there during the early morning in the lunar day before it gets too hot. It’s enough of a challenge to spend the entire lunar day (two weeks) there, as it gets very hot at midday. Then the lunar night, vert cold and no solar power, is another major challenge. And all EVAs on the Moon are dangerous too in the vacuum conditions, and we haven’t even been back to the Moon for decades. We just go back and forth to the ISS and do occasional spacewalks outside the ISS to repair it and such like.

After that, then we could explore the Mars surface by orbit, or from its two moons. But because of the risk of introducing Earth life, to confuse the search, then I think, if you love science, and think exobiology is important, it means we should hold off from sending humans to the surface. See also my President Obama - If You Love Science, Please Don't Rush To "Leap To Mars" With Elon Musk Et Al