If you hired a professional electrician, your wiring will be properly colour-coded. If not, it can be dangerous to assume which wire colour is live, neutral or ground. In Singapore the colour code for electrical wires can be found in energy market authority site (https://elise.ema.gov.sg/safety/about.html); whereas for colour codes used in other countries, you can refer to wikipedia (http://en.wikipedia.org/wiki/Electrical_wiring). In Singapore, the older code is as follows, i.e. the live wire is red, neutral is black, and protective conductor (ground/earth). The newer code is as follows, i.e. live (brown), neutral (blue) and ground (yellow-green). My HDB flat uses the older wiring code, whereas new appliances uses new ones.
To test which is live, there are two methods that I know. First is by using a test pen, and the second one is by using a VOM (volt-ohm-meter; or multimeter/multitester). The easiest would be to use philip test pen. There are other safer alternatives, e.g. multimeter, and non-contact test light, among others (wikipedia; http://en.wikipedia.org/wiki/Test_light).
FYI, while using my water heater, a loud pop sound and a foul burnt smell were detected. Next thing I knew, my water heater was not working. I bought a new one (with exact brand and model) and installed it myself. The water heater was not working. I tried to change the wall switch (dual pole switch), it didn't work either. In the end, called an electrician. He checked the whole thing and found out that the thing that burnt was the electrical cable. It was a 240-440 volt-ampere (1.8A) type. The load must have been too much and this caused the neutral wire to explode leaving black stain. He switched the cable to higher load type with thicker copper gauge.