What does filtered mean?

filter4dIt’s hard to beat the price of this filtered water bottle, available in 20-, 24- and 32-ounce sizes, all priced under $20.Although we haven't tested this bottle, our pros appreciateABSTRACT Lappeenranta University of Technology Department of Mathematics and Physics Idrissa S. Amour On Variational Ensemble Kalman Filtering Thesis for the Degree of Master of