Not sure if anyone noticed but the new WE prereq now uses 0.5 gpm for the baseline of restroom lavatories. This will make the mandatory 20% savings more of a challange. These are my calcs on the new baseline based on default use rates.
NA% - low-flow lavatory
0% - ultra low-flow lavatory
5.5% - low-flow shower
1.6% - low-flow kitchen sink
15.7% - low-flow WC
12.6% - dual flush WC
50.2% - composting toilet
7.8% - low-flow urinal
13.7% - ultra low-flow urinal
15.7% - waterless urinal
Since owners seem to hate waterless urinals to the point that I've seen them removed from a LEED building less then 1 year after occupancy I'm going to guess that the most common strategy for getting 20% water savings now will be low-flow urinals and dual flush wc for a total savings of 20.4%. Not too difficult.
I don't see how the 30% point is possible without the pint or waterless urinal and the 40% point will need the composting toilet. Unless I've missed my math. Or use of a grey water system can get the points. This might just spur more use of grey water systems.
Brenden McEneaney
Director, Northern CaliforniaCity of Santa Monica
47 thumbs up
September 17, 2009 - 6:41 pm
It is certainly more challenging, but it also can strongly depend on your occupant types. In a hotel project, you'll find that showers dominate water use (at least, the water use that's considered in LEED...). If you've got a lot of students/visitors, waterless urinals have a more significant contribution.
1.5 or 1.6 gpm showerheads are out there and are good.
For a typical office building, you might also go to the 1.0 gpf pressure-assist toilets. That makes 3.0 gal/day for female users vs. 3.2 with regular dual flush or 3.8 for commercial dual-flush. But it's still not 40% at the fixture level so you need to make up for it with the urinals.
I wonder where the occupant usage rate data originally came from. It seems like this might be an area for future research by USGBC to test and verify these assumptions, since they are the foundation for the indoor water usage estimates.