When planting potatoes you should plant them in moist soil.
So if you plant the seeds of the potatoes then you should water the seeds right after planting the potato seeds.
The same goes for potato plants you should soak the soil after planting either the seeds or potato plants and then 3 to 5 days after that first watering you'll need to water the potatoes again.
Just keep the soil for the potatoes moist and don't let the soil dry out too much but over watering them.
Potatoes do require deep watering though so that means applying enough water to moisten the soil 8- to 10-inches below ground.