The amount of Yields from potato plants are based on both the care your give your potato plants during the growing season and the variety of potatoes you choose to grow.
But normally you should get from 5 to 10 potatoes from every potato plant you're growing.
For young potato plants you should water them once every 4 to 5 days and for more mature potato plants they should be watered every 2 to 3 days when the tubers form.