Mistifarang on Thai electrical standards
First and for all I point at the Thai authorities, the Thai electricity suppliers and the manufacturers/importers of appliances to create and to allow very dangerous situations. Electricity is an energy one should treat with lots of respect and care!
I am quite a newbie in Thailand, but what I experienced and have seen until now shocked me and I took preventions not also to be 'shocked' by the electricity.
Indeed 'earthing' is an unknown field in this country. What I discovered in the house I rented was that an earth wire has been run to the central fuse box but the entire house has not been equipped by a single earthed socket whatsoever!
My blame on the manufacturers/importers of appliances is a serious one!
I just bought my domestic appliances and NONE of them was supplied with a proper Thai earth plug. NONE! Even not the computer and equipment. They were all equipped with the 'German' plug with side-earth connection used in a big part of Europe but not giving any earth protection at all in Thailand and are ruining the Thai sockets and especially the extension sockets with their very weak copper contacts.
Well, I thought, than fit Thai earth plugs and that's it! However, to find loose earth plugs is almost impossible. So, an ordeal to get everything safe!
The use of extension leads is almost a must because of the lack of sufficient sockets. When you choose leads with earth sockets you have to check careful if you choose the right one when you see three holes! Sometimes the earth has not been connected but has been made to let an earth plug enter. Fake safety! And check the plug at the other end of the lead if it is an earth plug!
The use of extension leads for the small Euro-plugs are creating another problem: the pins are too thin for the contacts, so sparks everywhere when connected or no contact at all, especially when you try to connect a Euro-plug with an adapter which can be quit heavy.
Concerning the use of a bathroom water heater without a proved proper earth connection I would say: avoid that risk! DO NOT USE IT. You are in direct contact with water and when the instrument fails you will be fatally electrocuted! Especially when it has been fitted next to the bathtub/shower as usual. Even when the hot water supply has a proper earth connection you cannot expect to be 100 percent safe. An earth connection creates safety but only because, in the case of a failure, the circuit breaker or fuse trips and cuts out the electricity. The response time can be quit long i.e. the time before cutting out can be too long. The best safety device for these appliances (and other) is an 'earth leak switch. These are responding within mills of seconds when due to a failure the electric current is exceeding 30 mA. (milli-Amps) for a standard switch. These devices do not need an earth connection so are very effective when you are in doubt concerning the viability of your earth connection. And they are responding much faster than a normal circuit breaker. Indeed they can trip easily in the event of a tiny failure in a cheap appliance but it is better not to be penny-wise-pound-foolish, so throw this appliance away as fast as possible!
When you have an accumulating water heater or a 'boiler' which has no proper earth connection you better pull the plug out before using the shower when you want to be safe.
To protect electronic equipment is much more complicated and this protection is not only solved by a proper earth connection, but better that than nothing. A protection with a UPS in combination with proper surge protectors are the only solution, however a protection against atmospheric surges entering through telephone- and electricity supply is not easy and cheap.
A big problem is the works sometimes been done by the electricity company in the main supply. I have seen more than once hugh damages to appliances due to switching-over tensions and not connecting the three phases in 3-phase-zero installations or changing the phase and the zero in such installations.