Feminine spirits of elemental energy, water weirds are soothsayers that offer knowledge of healing and cures, and answers to overcoming despotic governments. They appear as translucent, blue humanoid women composed entirely of water.
Their immature offspring, in contrast, are the most violent of the elemental+weirds, wrecking havoc and woe wherever they can. They often lurk in the regions of the Plane+of+Water bordering the Quasielemental+Plane+of+Salt, learning destruction before they learn to heal.
In return for their advice, they ask for rare items with healing
properties, the regalia of fallen tyrants, and secrets capable of
unseating whole dynasties.
Sources: Monster Manual (1st edition), Monstrous Manual (2nd edition), Planescape Monstrous Compendium Appendix III, The Inner Planes, Monster Manual II (3rd edition), Dragon #347