If you use a fish tank for wealth, it is to be placed in the wealth area of the living room or office.
Placing water to the left of the door is another matter, and that is when water is outside the home - it is best at the left of the door if you are in the doorway and looking to the outside. It sounds as if you have 2 ideas mixed up.
Thank you Lady moon for the reply. Can I know which is the wealth direction for 2011? Does it mean that I've to change the position of my fish tank every year since the wealth position will be different yearly?
You can do Feng Shui many ways. As it goes in a 20 year cycle,, find your wealth direction and you can keep the aquarium in the same place for the 20 years. Or, if you wish to change and update every year, that is also a choice. It is all up to you as to how you wish to use Feng Shui in your home. I go with the 20 year cycle as it is too hard to move it!