Feng Shui literally means 'Wind Water' so it's important to remember, when considering the Feng Shui of your site, the direction and location of the wind.
Often we forget about that and concentrate on the water aspect.
Also, often I read/hear others suggesting that water is good to enhance the water and wood elements but it will 'engulf' the fire, earth and metal elements.
Well, this is not true. Water will enhance all types of yang qi, so when using water, it doesn't matter whether it's for earth, fire, metal, wood or water elements, water will enhance and activate the yang qi.