CalGreen (more formally known as the Green Building Standard Codes) is the set of building codes approved by the California Bulding Standards Commission in reference to (in addition to many other aspects) the water conservation requirements of installed plumbing products. Products that meet these codes are said to be CalGreen Compliant.
California also has a separate set of legal requirements for the flow rates/water usage of plumbing products that were enacted when Governor Brown declared a state of emergecy in the wake of the California drought. As part of the California Energy Commission's Title 20 codes, these requirements refer to what products can be sold in California, based on their water efficiency. Qualifying products are referred to as CEC Compliant.
In sum, CalGreen and CEC Title 20 are different, and both must be followed in California. Note that not all plumbing products and product cateogries are under the purview of CalGreen or the CEC, and as such, these may be legally sold/installed in California. The requirements vary slightly, but here is an overview that will help your project stay compliant with both:
• Toilets ≤ 1.28 GPF, effective flush volume
• Residential Lavatory Faucets ≤ 1.2 GPM
• Public Spaces Lavatory Faucets ≤ 0.5 GPM
• Kitchen Faucets ≤ 1.8 GPM
• Shower outlets ≤ 1.8 GPM
• Urinals ≤ 0.125 GPF
Additionally, the total flow from all shower outlets per valve must be less than 1.8 GPM (i.e., shower design must either allow only one 1.8 GPM shower head to flow at one time, or multiple shower heads must still only flow a maximum of 1.8 GPM combined.