Our project is based on the case 2. Existing Site With imperviousness is greater than 50%.

We implemented several strategies for improvement:
a) Reduced runoff place
b) Accumulation of rainwater for reuse in toilet flushing

We calculate reducing stormwater runoff by reducing runoff coefficients. The result is an improvement of 12%:
Pre-development = 508,5 cf
Post-development = 447,2 cf

Then, we calculate the water reuse for toilet flushing in 72 hours. The result is 500 cf.
(The tank capacity is 1550 cf)

So, can we prove that our post-development runoff is 0 cf (447,2 cf - 500 cf)?