Unnecessary Permanent Irrigation

Our landscape designer has assured us that the native plant design will not require irrigation once established. The owner would prefer to install an irrigation system to use during the plant establishment, and then turn off after one year. Our project has a rainwater harvesting system that would support the irrigation needs. We already qualify for all 4 points: landscape design reduces the baseline "Total Water Applied" by 75%, and the remaining 25% is supplied from the cistern. The advantage we see is that if we can prove that less harvested rainwater will be dedicated to irrigation during the life of the building, more is available to flush toilets, and reduces the potable water use. Will the GBCI allow the installation of a permanent irrigation system that will be turned off after the first year of plant establishment? Or can we justify that the TWA would be reduce by x% after the first year, allowing us to dedicate a greater volume of harvested rainwater to flushing?