Hej! We are integrating a water tank in our project to supply the toilets with rainwater and to supply landscaping with water. We go for 40% water reduction and we also go for 2 points under credit c1 water efficient landscaping (that means water use reduction of 50% for watering of plants).
When we calculate with the LEED tools, we need 78 m3 (20 605. 5 gal) water for landscaping in July. When we calculate the water need for flushing the toilets with LEED tools, we need 191.5 m3 pr month (2298.5 gal), this is provided we use 50% rainwater for flushing the toilet.
With the help of our landscaping architect and our HVAC engineer we though calculated that a 210 m3 (55 476 Gal) rainwater tank should be enough to supply both toilets and landscaping with water.

The question is, does the simultaneity factor for water for toilet flushing and landscape has to be 1 with respect to the size of the rain water tank (based on values calculated with LEED tools)? Or is there at all a connection between credit 1 and credit 3? In Denmark almost everyone is on holiday in July, so there will be only 10 to 20% employees in the building which would logically result in a much lower need for water for toilets during July. Can we take that into consideration? I could not find any documentation on how this issue is handled under LEED.
Thanks in advance!!