A method is provided for treating at least a portion of a well. The method includes the steps of: (a) simultaneously introducing into a mixer at least: (i) a first stream comprising water; (ii) a second stream comprising a dry, hydratable, viscosity-increasing agent for water, wherein the second stream is substantially free of water; and (iii) a third stream comprising a non-hydratable, insoluble particulate; wherein at least the first and second streams are not mixed prior to being introduced into the mixer; (b) mixing the first, second, and third streams in the mixer to form a pumpable mixture, wherein: (i) the mixer creates at least a sufficiently-high shear rate to disperse the viscosity-increasing agent and the insoluble particulate in the pumpable mixture; and (ii) the pumpable mixture has or is capable of developing a substantially-higher viscosity than the viscosity of the first stream; and (c) introducing a treatment fluid comprising the pumpable mixture into a wellbore.