If the H2O is subsurface by more than a centimetre, then it is limited to the average diurnal temperature (broadly the mean of noon and midnight temperatures).

Since there is a 100 C temperature variation during the Martian Sol, then daytime temperatures need to be +50 C before buried water is liquid.

You can use brines to reduce this to about +30 C, but I thinl you'll find no records anywhere on Mars of this sort of daytime heat, except possibly in the polar regions.

There, we know there is extensive permafrost which cinducts heat well. In those areas, at depths of 10+ cm, you're playing a similar game of averaging wintetr and summer temperatures, and with winter at 147 K, you're on to a loser.

Did I say Loser?

I think for the sake of the civility of the board I'll end this "discussion". If you want to say more, come over to flame. It's warm enough to melt ice there, for sure...