The water you use to make espresso, in terms of hardness and quality, will make a big difference to the resulting taste. You should put fresh water from your tap (filtered if preferred) into the water tank of the Espresso Machine (maximum 1.4 litres).
IMPORTANT: Distilled water or mineral water can damage the espresso machine. Do not use either to brew espresso.
Tip: You can adjust the machine to suit the water hardness in your region by toggling between Low, Medium and High. Please see the related question for more information.