Water and Electric for some reason don't mix too well, actually quite a few Thais in Pattaya have died from badly installed shower heaters, not sure if any farangs have but wouldn't be suprised, now generally these accidents are caused by really crap wiring, ie no earth and stuff like that, so this shower is quite a classic example of what not to allow when you get your water heaters fitted.
In the picture you can see the shower head is actually above the water heating unit, it is about 15 cms away from it, the heater doesn't contain an earth leakage breaker as it is a cheap 3.5kw 2,000baht jobby, although 3.5kw is enough for most of the year and when it gets really cold just let it run for a couple of minutes or turn down the tap a little bit so less water passes through the heating element, also there are only 2 cables going into the unit, neither of these are green
they goto a normal breaker which is by the door on the inside of the bathroom, its a wet floor bathroom
Obviously the shower heaters are splash proof to a certain degree, but this is just way too close even if it was earthed, when the shower is on the water is going over the casing all the time
Here is a better shower unit, it is 3.5kw but does have an earth leakage breaker, costs less than 3,000baht and you stand a greater chance of coming out of your shower alive, which is always quite handy.
Also the mains breaker is just outside the bathroom door.
This picture shows that the water heater is well away from the shower head and will rarely if ever get splashes on it.
With the earth leakage breakers you are supposed to check them periodically, doubt many people do, so make sure it has a hard wired earth aswell.