Someone recently told me that lemon water can be hard on the teeth enamel. (My water is pretty alkaline spring water I think, so maybe that helps, maybe not.) Anyhow, the suggestions are:
Drink quickly rather than sip, to minimize contact with teeth.
Or, use a straw.
Do not brush teeth immediately after drinking lemon water, as tooth enamel is more vulnerable at that point.
So far I have not noticed any effects on my teeth, but (in case it makes a difference), I do not use toothpaste.
Christa Upton Black Hills Picture Books Edgemont, SD 57735