The inventions are for methods of forming and delivering a treatment fluid into a wellbore. In one aspect, methods are provided of treating a base aqueous solution to obtain a first aqueous solution, for example, to have a substantially reduced concentration of at least one component relative to the concentration of the component in the base aqueous solution, and using the first aqueous solution and a lower-quality water, such as the base aqueous solution, to form a treatment fluid. The first aqueous solution and the lower-quality water are merged after pumping the fluid portions toward the wellbore. The component is selected for being deleterious to the use or performance of a treatment fluid. More particularly, the component is selected from the group consisting of: a dissolved ion, oil, grease, a production chemical, and suspended, water-insoluble solids. This allows the use of lower-quality water for some of the water required for making up the treatment fluid.