This study is part of a Research project entitled: "Design Criteria for High Rate Filtration". The results discussed in this paper are aimed at identifying the parameters with the most important effects in direct filtration applications. The contribution of seven parameters involved in filter design and operation were assessed. The main results showed that the filtration rate, the media effective size, the media depth and the water head are the parameters that most impact filter performance. The contribution of each parameter depends on the performance angle to be improved. The contribution of the type of media and the uniformity coefficient is minor. For low turbidity waters (< 5 NTU), the raw water turbidity does not have a significant impact on filter efficiency. An increase in filtration rate helps increase filter productivity (effective volume of water per day), but at the same time it increases turbidity and particle breakthrough at the effluent. If high filtration rates are applied to very good quality raw water (low turbidity), then the quality of the finished water should not be compromised. Optimization of the main parameters is on the way. Validation will then occur using natural waters. Includes 14 references, tables, figures.