When first starting an exercise routine, some people may experience water retention, and become frustrated when they don't see the results of their hard work on the scale.
When the body is not used to being properly hydrated, it can hold onto water. Once your body is used to being properly hydrated, you will start losing fat at a healthy pace. Also, try to limit excess sodium in your diet and ensure you are eating nutrient rich foods. Proper recovery is also important to prevent the body from becoming over stressed and retaining water.
Finally, don't tell yourself the reason you aren't losing weight is water retention if in fact you just aren't making healthy choices in your diet!