If a small amount of deionized water remains in the Erlenmeyer flask during titration, it usually does not change the number of moles of acid or base present, so the titration result is generally unaffected. The main effect is dilution, which can make the endpoint color change a bit less intense and, in very precise work, slightly harder to judge.

What changes

  • The solution in the flask becomes more dilute.
  • The equivalence point itself does not move just because of the extra water, since titration depends on moles reacting, not the total volume of neutral water present.
  • The indicator may look paler, which can make the endpoint a little less easy to see.

What usually does not change

  • The amount of analyte present.
  • The volume of titrant needed to reach the endpoint, assuming the water is only deionized water and there is no contamination.

Practical takeaway

A wet flask is usually fine in routine titrations, but for best accuracy you still want the flask clean and free of anything that could contaminate the sample. Deionized water residue is normally acceptable because it only dilutes the solution, it does not add reacting ions.