To be a channel, you have to be निरासक्त - completely not attached to the family/person that you are helping.
A pipe does not keep any water or anything that it is channelling. If it does, we say it is dirty and don't use it until it is cleaned and is able to completely transfer its contents. It is the same with being a channel of prayers. You send prayers and you transmit healing or benediction. If you are not doing that cleanly, if there is even a little bit of attachment, the pipe and the channel need to be cleaned.
The water pipe does not see where the water is coming from, and it does not see what happens to the water after it leaves the pipe. It is natural to wonder. It is not natural to worry. It is definitely not ok to grieve if the water is not used properly.