Prepare your buffer solution, keeping in mind that a buffer consists or a weak acid or base and its conjugate base or acid, respectively. For example, if you want to make an acetic acid (CH3COOH) buffer, you'll need to have some of its conjugate "base," sodium acetate (CH3COONa), on hand to prepare a buffer solution. Be precise when measuring and adding components together, as the ratio of a the conjugate base or acid to its weak acid or base is central to determining the buffer solution's pH.
Distill your water by using a distillation apparatus if you don't have any distilled water on hand. Since deionized, distilled water has a neutral pH of 7, adding any quantity of it to a buffer won't affect that buffer's pH. If, on the other hand, your water is even slightly acidic or alkaline, it can impede your buffer's intended function entirely.
Transfer your buffer concentrate to a beaker or a Erlenmeyer flask. Measure the amount of water you need to use to delete your buffer solution carefully. (See Tips.) Add your water slowly, stirring as your introduce it to ensure that the solutions become fully incorporated and that you achieve your intended dilution.