The formula used depends a lot on the availability of the ingredients, their cost and the grower's experience. The mix that I am currently using is three parts crushed pine bark, one part perlite and one part Canadian peat. Much depends upon the type of potting mixture, humidity, light, temperature and air circulation of your growing environment. You must also consider the plants moisture requirements and whether you are growing indoors or outdoors. Generally, plants that are equipped with a cup should not be allowed to become empty.
Rain water is certainly best when it is available.
Those who grow outdoors during the summer will reduce the watering requirements and will provide the ideal humidity for most bromeliads. If you use city water and it contains excessive salts, flushing of the plant periodically will reduce the chances of salt damage. If you are growing indoors you need to mist the plant about twice a week in addition to your watering in order to prevent drying of the leaves by the low humidity. We have learned a lot about the light requirements of the various genera by studying their native habitats and from our own growing experiences. The beauty of most of the genera will be enhanced by giving them even more light than they would have received in nature.