Effervescent? Your question is ambiguous. Do you mean will it ruin the effervescence or the vitamin?

The water will still effervesce.

Ascorbates do break down in hot water (and UV light and so on) but how hot? Hot enough to make tea, or hot enough to strip paint as a stream of pressurised steam? Water near the boil would break some down, but not a great deal all at once. If you prefer to drink your Vit C warm in cold weather that should be all right, but the hotter you add the water and the longer before you drink it, the more Vitamin you lose.

However, such a tablet contains so much more Vitamin C than you need, that I cannot get too excited about it.

But why you should want to do that , I can hardly imagine!

A votre santé

Jon