Any surface water on Mars would evaporate or freeze due to its atmospheric pressure only being 0.6% of Earth’s. Having a thicker atmosphere would keep water in a liquid form and trap other gases required to make Mars habitable. Ideas to thicken the atmosphere center on unlocking CO2 either by nuking the polar caps or extracting CO2 from the soil. But this would likely only increase the atmosphere to 7% that of Earth.
(https://bit.ly/3eQDFCV, https://go.nasa.gov/3eLxcc2)