The lack of liquid water on the surface of Mars is one of the major roadblocks to permanent human colonisation of the planet, but there have been discussions about how to tackle this problem. Since we know that Mars has plenty of water in the form of ice, colonists could place their bases primarily in these areas. Another possibility is creating the right conditions for water to reform.
Terraforming, a process designed to create a habitable planet by altering its atmosphere, surface and other properties, would be the obvious course of action to take. If we could give Mars an atmosphere, surface temperatures would rise and theoretically we’d naturally end up with liquid water. We’d also need to be able to sustain that heat and keep the atmosphere stable. However, terraforming is still a theoretical process and comes with numerous challenges.
The water issue is also just one of many when it comes to colonising the planet. That said, making Mars habitable is still very much within the realm of possibility.