Kettles
Always use fresh water to fill kettles, re-boiling water will encourage the build up of limescale and other deposits which can lead to a taste in the water.

Boilers and Central heating
Keep the temperature setting below 60°C. Scale build up usually occurs when the temperature of water reaches 71°C.

Washing machines
Keep the door open to air the inside of the machine. If you set your machine on a low temperature cycle to save energy, run the machine on a 60°C wash every so often to help avoid bacteria and mould growth inside the machine.

Shower curtains, tile grouting and taps
To prevent discolouration due to mould or fungus, clean these areas regularly with a household disinfectant or bleach. Air the kitchen and bathroom regularly, opening windows or using extractor fans.

You can read more here about keeping water safe.