If this is water that's from the fresh mortar, because the block has just been laid, there's nothing you can do but be patient.
Trying to speed up the cure time will cause cracking and weaken the mortar.
If this a block structure that's been open to the elements for a while, you can use a dehumidifier.
If the building is large and you can vent it, use a "Torpedo" type gas heater.
Be very careful with a gas heater. You can burn up all the oxygen in the room and/or cause dangerous levels of carbon monoxide. Do not use this in a closed space.
It can also be a source of ignition for paint or solvent fumes or other flammable materials.