Homeopathic pills are usually literally sugar pills, essentially small crummy candy, so not really any water, despite the purported basis of the "technology".

Sure. Sugar allergy is a thing too.

If you give me six lines written in a material safety datasheet for the most chemically inert of materials, I will find something in them that could cause some human, in some situation, to die.

After a little bit of googling, it seems that sugar allergy from ingestion doesn't exist. Intolerance is not allergies.

I did find that there's apparently one case of anaphylaxis caused by injection of fructose, though it wasn't the normal reaction referred to as allergies.

Water allergy is a skin condition triggered by contact with water. I don't think that applies to swallowing water.

If someone's actually allergic to water, they're going to be reacting all the time since they're mostly water and have to drink regularly to stay alive.