This paper presents a dimensional analysis for determining optimal flow discharge and optimal penstock
diameter when designing impulse and reaction turbines for hydropower systems. The aim of this
analysis is to provide general insights for minimizing water consumption when producing hydropower.
This analysis is based on the geometric and hydraulic characteristics of the penstock, the total hydraulic
head and the desired power production. As part of this analysis, various dimensionless relationships
between power production, flow discharge and head losses were derived. These relationships were used
to withdraw general insights on determining optimal flow discharge and optimal penstock diameter. For
instance, it was found that for minimizing water consumption, the ratio of head loss to gross head should
not exceed about 15%. Two examples of application are presented to illustrate the procedure for determining
optimal flow discharge and optimal penstock diameter for impulse and reaction turbines.