To vacuum water with a Ridgid wet/dry shop vac, remove the dry filter, ensure the tank is empty, and after verifying the vac is suitable for wet use, suck up the water, then empty the tank immediately after.
To vacuum water with a Ridgid wet/dry shop vac, you should first ensure the device is designed for wet pickups, as not all models are suitable for this purpose.
If it is, then you start by removing the filter inside the vacuum, because using a filter designed for dry debris can damage the vacuum when sucking up water.
Next, check that the collection tank is empty and that the vacuum is unplugged before you start. When you're ready, plug in the vacuum, turn it on, and place the nozzle into the water you want to remove.
Move it around until all the water has been vacuumed up. After finishing, turn off and unplug the vacuum, then promptly empty the tank to avoid mildew or unpleasant smells.