The source of water (feng shui) is an important consideration when selecting water for tea. The source of water dictates its content because content reflects its source. Remember that water isn't man made, all water comes from nature, carrying with it natures signal. Therefore the source of water can tell us a lot about the content, properties, and qi of that water.
Water can either come from a natural or artificial source. Depending on where the water comes from certain things have to be considered. If the water comes from an artificial source you will want to consider how it is treated, how it is delivered to your house, and if it is filtered. Once water is treated its essence changes. If treated with chlorine it is imparted with an odour and taste. This water is not suitable for tea. Conversely, if the water is treated with ozone the essence of the tea isn't degraded. Tap water is water that is active because of its movement through pipes to your kitchen. The movement is good and stirs and activates the qi of the water but most cases this is overshadowed by taste and smell and the removal of important minerals from the water. Many people filter the tap water before they use it for tea. The problem with this is that other important things besides taste and smell are also removed from the water.
Water from natural sources have not been degraded or stripped of its qi and therefore is optimal for tea. What natural source we chose can be a difficult decision. We should first consider the waters proximity to where we live. Ideally the water should either harmonize with the tea or harmonize with the drinker. It will harmonize with the tea if the water is from the same geographical location as the tea. It will harmonize with the drinker if the water is from the same geographical location as the drinker. Unless you are living close to the actual area where your tea is grown, economically it makes no sense to acquire water from this source. It makes much more sense to acquire water from a local source. The closer the source is to where you live the closer it will harmonize with you. This also can be very practical as the closer the source the cheaper and less time consuming it will be to acquire.
"Water from a mountain-peak spring is pure and light" - The higher up or higher the mountain the spring is found the more yang or energy is contained in this water. It is though to be very active (yang) water because it has come from a source so low to a place so high. It is thought of as pure because it is closer to heaven, also because it has not been contaminated by anything by flowing downstream. It is considered light because it has the ability to climb, or float up to such great heights, also maybe water that comes from the high mountain is less likely to be as hard. This type of water has strong pure yang energy.
"water from a spring at the foot of a hill is pure but heavy"- It is still pure because it came from the mountain, a symbol of purity, and divinity. Also as stated above it has not been contaminated by anything flowing down stream. It is considered heavy because it doesn't have the ability to climb, it is weighed down and flows from the mountain at a low altitude, also maybe water that comes from the foot of the mountain is more likely to contain more mineral deposits and salts (it is heavier). This type of water has strong pure yin energy.
"water emerging amidst the rocks is pure and sweet"- It is pure because spring water from rocks is closest to its source, it is sweet because rocks are considered the truest Earth. Earth's taste is sweet. This type of water is more yang in nature, but it most in harmony with Earth.
"water emerging from sand is pure and cold"- It still remains pure because sand acts as a filter, also because sand sinks to the bottom and doesn't contaminate the water which is drawn from the top. The water is considered cold because sand sinks and is small and course it is therefore considered to be yin in nature. This type of water is more yin in nature.
"water emerging from soil is bland and plain"- It is bland and plain because soil leaches out the waters minerals. It also has the potentiality to be impure. This type of water contains no essence.
"water flowing from yellow rocks is good"- Yellow is the colour of Earth. Yellow rocks indicate water that is most in harmony with Earth.
"water draining from dark rocks cannot be used"- Dark (Black, or even deep blue) is the considered the most yin colour. Dark colour rocks indicate that water contains too much yin energy and not enough yang and therefore will not be active enough to bring out the essence of the tea.
"flowing water is better than still water"- Flowing water is active, yang, while still water is inactive, resting, yin. Active yang type water is best to bring out the essence of tea. Still water has not the energy to do so as effectively.
"water emerging from a shady place is better than a sunny place" - Shady places are more yin, sunny places are more yang. Sun causes the water to accumulate algae, therefore water should never be exposed to light.
"Mountain water is superior, river water is less good, and well water is the worst" - Mountain springs have more potential energy, and yang, as they are located high above. Streams have less potential energy, but still flow pretty strongly, and have a current. Well water contains the least qi, vitality, or yang as it contains no potential energy, is still, and lies low. Well water contains the most yin energy.
"if no river water is nearby and no mountain with a spring of water, one should use only water stored from the plum (monsoon) rains of that spring season since its flavor is sweet and harmonious; it is the water that makes everything grow" - if you are going to use rain water, the rainwater that harmonizes the closest to the energetics of tea is spring rainfall that occurs just as the first blossoms of spring are emerging(or the first tea buds). This water is thought to have abundant qi because it nourishes the abundant spring growth. From a astrological perspective, it shares the same energy of the tea that is also fed by these same rains as they sprout from the tree in early spring.
"Water from melted snow is clear but feels heavy and dark." - the qi of water from pure melted snow (collected in the winter) is "heavy and dark". This is due to this water harmonizing with the energy of winter which is the most yin time of year. It has the least daylight hours, so is dark. The water is considered heavy because it comes from the snow which is dense and heavy and cold in nature.
Overall these passages speak to tea in general but are more specific to green tea or other light teas. If you are trying to harmonize the water to a heavier, darker tea. Water from a spring at the foot the mountain or from an artesian well is also appropriate. If you are trying to harmonize the water to a medium, neutralizing, or regulating tea, water from the middle of the mountain is also appropriate.
It is also very important to consider the environmental cost of the water you use for tea. If the source is far away and you must ship the water long distances the environmental impact is enormous. This completely contradicts the reason we chose that water in the first place, harmony.