Since they are both part of the five elements and are used to remedy certain situations in the greater environment, they need to be placed very carefully. Water in the west is not good, while in the southwest and east it can assist prosperity, during this time period. These directions should not be in front of, or behind the house or building. If they are, it takes a qualified practitioner to determine if the water will have a positive or negative effect. If you are striving for the effect of the water element, then it is better to not use an earthen container such as a fountain made of rocks since earth blocks water in the cycle of the elements.
Metallic containers work well as metal strengthens water.
I have seen my clients use metal troughs effectively with beautiful plants and flowers planted around it to blend it with the environment. Ponds and pools can be used if placed under the guidance of a trained Feng Shui practitioner. The same can be said of rocks, especially large decorative rocks. Because these are used in certain situations to correct for a problem, they need to be placed under the guidance of a Feng Shui practitioner. Placed haphazardly, they could have an adverse effect on the prosperity of the building if used in front of or in back of the structure.