deionised water is highly recommended to prevent any possible contaminaion

If your particular Ab-target interactions are partly based on the ionic strength of the solutions you use (which, in IHC theory, it often is), then, you want to have full control of the ionic strength of your solutions.  Thus de-ionized water will be the better choice.  Although distilled water might be OK in your situation, you won't know until you try it. It's a gamble though...

De-ionized water should be always used in IHC, particularly if your IHC results must be compared with qualitative or semi-quantitative approaches. However, in other cases, distilled water can be used if de-ionized one is not available, always considering this aspect during microscope observation. 

We use distilled water all the time for IHC. Just be sure that the pH of your buffer is at the correct range.

Distilled water for IHC can be used without any problem.

Be sur that all yours buffers are at the good pH.

Best regards,

VM

We use distilled water for our wash buffers and rinses in all IHC stains, it's fine.

We use distilled water for IHC, just make sure that pH value of your buffer is correct. . Don´t have any experience with de-ionized water for IHC.

We have used both for IHC. Initially our provider was DAKO, and their advisers told us to use deionized water. Nowadays we have ROCHE equipment and work with distilled water.

I have used both distilled & deionized water. The pH of the buffer is important. If your positive and negative control slides are working well with distilled water then distilled water is a good alternative.