The quality of water plays an essential part to the quality of coffee. Not only coffee, but also all the high-quality drinks are demanding to the quality of water. Scotch whisky is hailed as "the water of life", it must be made by the native unpolluted water.
The paramount factor is unpolluted water, because unpolluted water is healthy for people to drink. And the water should be fresh, the stale water exposed for long time is not available to be used for making coffee. Next, water can not be blended with other odors which will damage the taste of coffee. Last but not least, water should has proper pH, neither acidic nor alkaline.
Besides one way valve recommends, the temperature of water is also influential to the quality of coffee. Generally, the temperature of water to brew coffee should be 91℃ to 94℃, this range of temperature is the optimal temperature. If the temperature of water is too low, the coffee will have apparent acid taste; if the temperature of water is too high, the coffee will be apparently bitter. The temperature of water is certainly changeable and different situations should be taken into account. For example, the dark roasted coffee beans should be used water of low temperature to brew while the light roasted coffee beans should be used the water of higher temperature.