Most Feng Shui enthusiasts know that it is favorable if a house is backed by a hill or higher land and faces water (e.g. lake) or a lower terrain. Such a configurable is good for money, relationship and health luck.
The reverse, Back Water Facing Mountain is unfavorable and suggest obstruction ahead without support that can lead to a decline in fortune.
While it is favorable to have mountain for support at the back and water in front suggesting a clear unobstructed path to money, I would like to suggest some qualifiers.
First the mountain at the back cannot be too near or too high. Otherwise it becomes a sha. Secondly the water at the facing cannot be too near or slopes down excessively which can result in health problems.
Finally the mountain at the back should be covered with lush greenery which indicated the presence of strong qi. In Feng Shui such as mountain is known as a Green Dragon and is revered.
A mountain that is bare or rocky with sparse vegetation or with rocks jutting out is not favorable and is known as a Sick Dragon. It is considered a sha and can depreciate the quality of the house, most of the time with problems affecting relationship and health.
It is also unfavorable if the house is located very close to a cliff. In Feng Shui, this is known as the Head Pouring Water sha as water can fall off the cliff onto the house causing damage. It also does not take much common sense to know that water and mud can fall on the house and when there is a mudslide and bury the house.
A house should also not face a long downward sloping road at it may cause money loss and health problem related to the lower abdomen.
What about if the land on the left or right is higher that yours? It is not a problem if the difference in the height between the land (and the house) on the your left and right is small e.g. 2 feet. However if the difference is great then the Green Dragon and White Tiger comes into play.
Traditionally the Green Dragon is associated with the male and is auspicious while the White Tiger is associated with the female is considered inauspicious (though I do not totally subscribe to this belief).
The left side when looking out of the house is the Dragon side while the right side is the Tiger side. Conventional thinking prefers the left side to be high so that it benefits the male in the family. Traditionally it is the male the brings the bacon home so benefiting the male makes sense. However in modern society, females contribute significantly to the family too and nowadays (at least in my opinion) it is okay too if the Tiger side is slightly stronger.
But why was it considered inauspicious. I suppose in a male dominated society if the woman in the house is too powerful or dominant, it is inauspicious!
Today? Perhaps not!