Systems in the California and Desert Southwest regions all showed the characteristic gradual decline in performance described above. Regression slope and R2values for all systems in these regions were summarized and checked for quality. Any system with an R2 value less than 0.7 was excluded from the rate analysis. A total of 46systems remained in the data set after all systems in regions with frequent rain and all systems with unacceptable curve fits (R2 value less than 0.7) were excluded. Each of these 46 systems was categorized by its region and environment.