After the quality of the tea you're using, water is the second most important factor in the eventual taste of your brew. Just like a fine whiskey, brewing a great cup of Chinese tea requires good ingredients and clean, clear water.
The right temperature of water varies depending on the type of tea - roughly speaking, dark teas like Lapsang Souchong should be brewed with boiling water, and green teas like Long Jing should be brewed with slightly off-the-boil water (around 80-90 degrees) - check out our brewing guides for details.
Green teas have undergone less processing than their roasted, red cousins and they reward a lighter brew. Using cooler water will allow the more lighter, subtler flavours to come to the front, instead of being overpowered by all the natural elements that are released with boiling water.
The quality of water coming from your taps or kettle plays a huge part in the taste of your tea. Serious enthusiasts only use bottled mineral water to brew their tea, so if you're tea obsessed, consider buying a water cooler and keeping it stocked with fresh water.
Alternatively, if you're from a extremely hard- or soft-water area, you might want to use a water filter before you brew your tea, and also regularly clean your kettle and keep it free of limescale. In London and most of the UK, the water is relatively hard, meaning that you will really notice the difference between a tap-water cup of tea, and a filtered-water cup.