In the Eastern Seaboard area it is not normally advised to drink "Tap Water". Some hotels may have filtration systems that can dispense potable water to your room. Most visitors and Thais used bottled water which can easily be bought in convenience stores or supermarkets. Sometimes when you have your own container it may be convenient and probably cheaper to buy your water from a coin operated drink dispenser (See Photo) which are sprouting up in even remote villages. It is advised always to carry an adequate drinking water supply, particularly in hot spells, to avoid dehydration.
Thailand uses the 220-240 Volt system familiar to mot European countries. The connecting plugs are normally two pin versions, Flat pins tend to be the norm and it is not common to find the three or round pin types. Therefore it is sensible to bring a convertor/adaptor. If you have any difficulty, the appropriate adaptors can be found in most hardware stores.
The Kingdom has a nationwide network of land lines, although, because of the recent rapid growth in the mobile sector most of the maintenance spend is aimed at improving mobile communications. Development of the 3G network is underway and bandwidth is limited by the distance from Bangkok.
It is often possible to purchase a Thai sim card to avoid excessive roaming charges ; particularly if you intend to travel outside the main Urban Centers. The main operators (AIS, DTAC and True) all operate different rates and services. The most popular system is to use a pay as you go system where recharges can be purchased from mini-marts or convenience stores.