Water-based ink works its way into the fabric instead of forming a layer on top, so a print on a light cotton tee can feel like part of the shirt. Curing happens in two stages. Every bit of water has to leave the print first, and only then can the ink climb to the temperature its binder needs, which is why these prints spend longer in the dryer than plastisol.
Standard water-based colors are fairly transparent, which suits white, natural and light garments. On darks, printers switch to high-solids opaque versions, print a soft white underbase, or use discharge ink. The ink can dry in the mesh during pauses, so it needs a water-resistant emulsion and a press operator who keeps the screen flooded.
Worth asking: how the shop confirms cure on water-based jobs (usually with a wash test) and whether your blank's color and fiber suit the ink. The screen printing inks guide covers every option in depth.