Distilled water can not be PH balanced. It has nothing to stabilize the water, no Ions = no balance if you are using distilled please put at least 1/4 strength nuts then Ph balance.I bought some distilled water for ph calibration but also in case i needed to water it with nutrient free water.
If you are flushing with it then you don't have to but I would still recommend so, this will help also with ph balance the soil/medium.