The standards are constantly changing but generally today, everything must be on an earth leakage and everything should have a ground wire.
Your geyser should have a ground wire for sure and in new installations it must be on a earth leakage.
Additionally the copper piping on the geyser must be
bonded (meaning earth wire is connected to it).
Your installation ideally should be:
Main switch -> Earth Leakage 1, Earth Leakage 2, ...
Earth Leakage 1 -> Geyser + Stove + Oven
Earth Leakage 2 -> Plugs + Lights
If you have 3 phase, things get different.
You can even put every circuit on a separate earth leakage.
In the UK they have started selling a combined earth leakage and circuit breaker that only takes a single space in a DB. Very cool because it allows every single circuit to be on an earth leakage.
The reason it is better is that an earth leakage will trip on any leakage of current (well more than 30mA). So you can get into a situation known as nuisance trips. The fewer earth leakages you have the higher the chance of a nuisance trip, and the more annoying it is (eg. single earth leakage means your entire house is without power)
EDIT:
Also earth leakage and earth wires don't have much in common despite the name.
The earth leakage measures power flowing between live and neutral and trips if they aren't balanced.
Earth wires allow a safe and low resistance path for current to flow in the event that a conductive material comes in contact with live.
The earth wire allows the current to flow from the live to earth thereby causing a earth leakage to trip, but in and of itself, it doesn't actually play a role in how an earth leakage works.
Also your lack of knowledge is so bad that you'll screw this up. I'm not going to withhold knowledge but I'm just telling you. You'll f#@k this up. Either hire someone or else download the SANS documents and study them in detail. I did the latter myself.
