The FTE occupancy number you use must be consistent with the FTE occupancy numbers used in all your other LEED credit submittals, including: 

WEp1: Water Use Reduction
WEc2: Innovative Wastewater Technologies
SSc4.2: Alternative Transportation—Bicycle Storage and Changing Rooms
SSc4.3: Alternative Transportation—Low-Emitting and Fuel Efficient Vehicles
SSc4.4: Alternative Transportation—Parking Capacity.
WEc4: Process Water Use Reduction

The FTE occupancy number you use must be consistent with the FTE occupancy numbers used in all your other LEED credit submittals, including: 

WEp1: Water Use Reduction
WEc2: Innovative Wastewater Technologies
SSc4.2: Alternative Transportation—Bicycle Storage and Changing Rooms
SSc4.3: Alternative Transportation—Low-Emitting and Fuel Efficient Vehicles

SSc4.4: Alternative Transportation—Parking Capacity.

Determine the number and types of occupants in the building. The water-use calculations are based on occupant use and the number of full-time equivalent (FTE) occupants, including employees and visitors—not the number of water fixtures. 

Check for local incentives through municipalities and utilities that reward or encourage water-saving strategies—as well as restrictions that may apply. Rebates are common, as are plumbing codes restricting certain water-savings technologies such as waterless urinals, graywater reuse, onsite wastewater treatment and reuse, rainwater harvesting, composting toilets, and other strategies. See Resources for more.

Check local codes and restrictions. Throughout the U.S. there are widely varying laws addressing water use, and many states have very different approaches to rainwater collection and greywater/blackwater reuse. 

Consider occupants when debating whether to use graywater or waterless and/or dual-flush fixtures. Cultural perceptions of these types of applications may need to be evaluated to gauge whether they will be successful in your building. It is also a good idea to have education outreach in order for building occupants to know how to use the new fixtures and to understand the importance of water reduction strategies.

Graywater and rainwater collection systems can offer a potential non-potable water source for interior applications. However, you may find that it is easier—based on code issues and simplicity of system design—to direct reused water to an irrigation system or cooling tower. All solutions should be viewed in the context of finding the best whole-system approach for building and site water use.

Well and pond water are not considered “reused” for the purposes of this credit and must count as potable water—so you don’t get credit for substituting them for conventional water sources. Water types that do count as reused are: 

Rainwater;
treated wastewater supplied by the municipality or water utility;
graywater coming from onsite lavatories, sinks, and showers;
treated blackwater;
rejected water from a reverse-osmosis treatment process;
sump-pump water;
air-conditioning and cooling tower condensate.

Consider replacing potable water use with alternative sources such as collected graywater, rainwater, municipally supplied treated wastewater, or wastewater treated onsite for reuse.

Are composting toilets an option? While not common, composting toilets are waterless fixtures that go a long way toward achieving this credit. However, they do affect programming and layout, so consider them early in the planning stage.