What if this or a similar product was installed? It is a Kohler company.
http://www.mirashowers.com/onlinecatalog/pdf/1062246_w2_b.pdf
"It is recommended that a non-restrictive (free flowing) isolating valve is fitted in the cold water supply pipe to allow the complete maintenance of the appliance. Do not use a valve with a loose washer plate (jumper) as this can lead to a build up of static pressures."
"Supplementary bonding: Within the bathroom or shower room, all accessible conductive parts of electrical equipment and extraneous conductive parts (metal parts) that are likely to introduce earth potential, must be electrically bonded to earth using a minimum cable size of 4.0 mm2 if the cable is not mechanically protected, (2.5 mm2 if mechanically protected)."