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When performing a titration, once the acid/base in the burette is slowly released into the conical flask, it may splash onto the sides of the conical flask. It is then advised that we wash the sides of the conical flask with deionised water.
Will this not affect the concentration of the acid/base solution by decreasing its concentration and therefore it will take less volume from the burette to change the pH indicator?
In short: a small quantity of additional water will not alter the quantity (moles) of $\ce{OH-}$ of your lye, or $\ce{H3O+}$ of your acid to be characterized. But it will dilute the intensity of the colour of your indicator used; this then hampering the visual inspection of your analysis.
True, the addition of additional water to rinse off the drop from the wall increases the total volume of your analyte, and this will lower the concentration of the acid / base to characterize. Thus, aim to titrate without splashing the reagent solution to the beaker's wall. It takes some practice to swirl the Erlenmeyer flask such that analyte and reagent solution are mixed with minimal splashing.
The deionized water you already used to dilute your analyte however is neutral; i.e., it neither should be acidic, nor basic. Overall its use will add as much hydroxy $\ce{OH-}$ as hydronium $\ce{H3O+}$ ions. Thus, the consumption of reagent solution is not affected.
