The next component is vital to a good cup of coffee: What type of water are you using? Brewed coffee is over 98% water, so it stands to reason that the better water you use, the better coffee you get.
Hard water simply means water that contains minerals, such as tap water. While hard water can lead to under-extraction, overly hard water can cause problems with your equipment due to calcification. This will also affect the taste of your coffee. In general, 3-6 grains of hardness is considered an acceptable amount.
Tap water natually has minerals in it. Depending on where you live, the mineral content can either have an adverse or positive affect on the water, and by extension, your coffee. If the water is over-saturated with content, mineral or otherwise, it will not be able to absorb anything. In other words, it won't properly extract coffee flavour, leaving you with a weak, underdeveloped cup.
Soft water refers to the absence of minerals. A good example is distilled or reverse osmosis water, which are stripped of all minerals. Water that is too soft leads to over-extraction, so is unsuitable for brewing coffee.
Generally, falling rain contains no calcium, so it is considered soft water. However, once it starts to pass through the soil and rock bed, it absorbs minerals, gaining in hardness. It's probably best not to use rain water for brewing your coffee.
Best practice is to use freshly drawn, cold water, passed through a carbon filter system to remove any unwanted impurities.
Now that we know the best water to use, let's consider how much water and coffee to use