Ohmic probe a inssues water table

Water is always a challenge for ohmic sensing.

Assuming you used the circuit from the diagram that is floating around the forum for THCAD ohmic sensing, then replacing the 24K resistor with a lower value will help make it less sensitive to water.  I don't run the THCAD ohmic sensing anymore, but I do run a 100 ohm 7W resistor.  It definitely helped make it less sensitive to water on the plates.  I think Phill runs 3x 100 ohm 10W resistors twisted in parallel to give 33.33 ohm of resistance.  

That said, I rarely have a "wet" plate while sensing.  I make sure to squeegee off any water before starting my cuts, and the air between cuts keeps the water away from where the next cut will take place.  I imagine every plasma cutter has different post-flow air settings, so if the air is off before the next cut, you might try a longer post-flow (if it's adjustable) to help a bit. 

The only difference is the sensitivity.
I ended up with 3x100Ω during testing and was too lazy to remove them when finished. 
I have left them as is to see if there are any detrimental effects.
On a table I think 1x100Ω would be quite adequate as the post flow of air from the previous cut will normally remove most of the water.

Yep, what Phill said...

I tested with 3 100Ω resistors that were not high enough wattage, and ended up with 1 100Ω resistor because I honestly just forgot what I had there when I ordered the resistor (from work).  My brain let me down

I haven't had any trouble with the one 100Ω resistor.  As Phill said the post flow keeps everything dry anyways.  Highly recommend the relay method.  It's been great.