If you need to add cold water to your bath or shower, your geyser thermostat temperature is set too high and it's wasting energy.
Your geyser accounts for about 30-40% of your electricity bill. There are various ways to reduce this -- apart from using less hot water of course -- but simply turning the thermostat down to between 55-60°C can make a significant difference. Keeping it above 60°C is unnecessarily high for a hot shower (or occasional bath, if you must!)
If you're uncertain how to turn down the thermostat yourself, it's probably best to ask an electrician or plumber to do it next time you need to call one out. If you want to try DIY:
Turn off the electricity supply.
Find the geyser, usually in the ceiling.
Open the protective covering over the thermostat.
Turn the thermostat setting to between 55-60°C. This might require a screwdriver.
You may have to try different settings until you get one that suits you.
- Olivia Rose-Innes, EnviroHealth Editor, Health24, May 2012