A picture would help us out a lot here. Bromeliads for the most part just 'hang on' with their roots, that is, the roots hold them in place and upright but they collect nutrients and water mainly through the leaves. So there probably isn't any need to try to root it in water. It might even rot the plant if the base of the leaves is in water for too long. Just set it on some firm, moist medium - a piece of bark, a small branch, a stump or a log - and it will grab hold.
You should maybe wait until you see some little threads on the pups before you detach them from their mama. The guideline is to usually wait until the pups are roughly half the size of the adult plant before removing them.
