How can one get dietary "fiber" from a psyllium that mixes with water?

It is still there. When you mix the psyllium in water, it is still there, same as when you add sugar to your coffee--it dissolves in the coffee, but it is still there. Also, it would be difficult to consume dry psyllium powder/husk. So, drink you fibers to good health. Any concern, consult doc. Good luck.