If you're looking for anime similar to Nadia: Secret Of Blue Water, you might like these titles. All recommendations are made by Anime-Planet users like you!
Having lost her mother at birth, Jane Buxton grows up with her brother George the dreamer and her moody step-brother William. George sets off to seek a legendary 'floating liquid' that he hopes can revolutionize transportation and bring about human flight, but word soon returns of his tragic death. Convinced that her brother is still alive, Jane courageously sets off to find him, and encounters a world of adventure.
Nadia and Secret of Cerulean Sand, are both family friendly adventures set in the past.
They also both have a set of young main protagonists, that are part of a larger team set up on a mission.
The similar themes do not stop there. The two shows have amazing machines that stretch the possibility of inventions far beyond thier years, but use materials that would have been readily available. Wood/Rivets/steam engines.