29 Sivan 5713.
...I was pleased to read what you wrote regarding the mikveh, that everything is good. However, it is surprising that you did not mention in what manner the waters were gathered—whether they are rainwater or otherwise—as I have already written to your honor previously. Certainly, you will clarify this in your next letter...
Summary
The Rebbe emphasizes the importance of specifying details about the source of mikveh water, highlighting careful adherence to halachic requirements.