Found this Laser Machine MaintenanceLaser power and the machine body must have good grounded power connection. The earth wire should be connected between the power transformer and the machine grounding connection.
A good grounded connection is great for the following reasons:
A good grounded connection will assure the laser power to work normally
A good grounded connection can extend the life of laser tube
A good grounded connection will prevent any other electrical interference which can impact the outcome.
A good grounded connection will prevent any electrical damage to the machine.
Please make sure to ground the machine properly!

Also I would think that a large amount of static would build up when cutting plastics if the laser was not grounded. Watering the earth stake that's something I've never heard of, besides most household earths have been on PME for the last 30 + years.