Why Grounding Matters
Under-sink heaters and dishwashers are Class-I appliances in a wet environment; without a ground, a failed element can energize the casing and the water stream.
Solution 1: Extend PE from the Panel (Best)
Run a dedicated 2.5mm² green-yellow wire from the PE busbar of your distribution box.
Solution 2: Rewire the Circuit
During renovation, replace with 3-core cable and proper grounding — the cleanest fix.
Solution 3: Local Equipotential Bonding
As a stopgap, bond the area equipotentially and add a 30mA RCD plug.