Single amaryllis need around 8 ounces of water when starting to grow them.
Then after the amaryllis grows you can increase the amount of water that the amaryllis will get.
As the amaryllis plants grow you can give them 10 to 12 ounces of water per watering.
You should also use room temperature or tepid water when watering your amaryllis to prevent problems with the plant.
Too cold of water may harm the amaryllis so let the water get to room temperature before watering them.
You should only need to water the amaryllis every 3 days or so unless the soil gets too dry then water it more often but don't over water the amaryllis otherwise it could kill the plant.