You need to check with your council whether they have rules about the use of discharge water.

If they give the ok, then you need to check with your local garden centre on the impacts on your plants, before you use the water. Why? Discharge water from evaporative air conditioners contains concentrated levels of mineral salts. Generally we expect the water discharged to be fine for your garden, unless your water supply has a high mineral salt content and/or you water management system is set to discharge infrequently.