How can you pour so much water onto a sheet pan without overflow? Recipe omits putting potatoes on a sheet pan too.

The second direction in the recipe directs you to add the potatoes to the sheet pan, then season with the oil and salt. The amount of water is not excessive either, and just about any rimmed sheet capable of holding that amount of potato will hold it easily. If you are nervous about transferring the sheet with water to the oven, simply put the dry filled pan on the oven rack first, and then pour in the water.

It's not that much water (1.5 C). I put the half sheet pan with the seasoned potatoes in the preheated oven then add the water with a measuring cup so no worrying about sloshing it around.

Average half sheet pan at 18 x 13 x 1 inch = 234 cu in = just over 16 US liquid cups.
Enough to hold the potatoes and water called for?