I need to learn what?

It's one of those names of radicals that have nothing to do with what they actually are, such as 雙人旁 (彳), 左耳旁 (as in 陽).

BTW, you can call it 四點火.

Thanks for the warning about the other radicals! I assume somewhere there is a list of what Chinese "commonly call" the various radicals, vs what they actually mean?

There seem to be quite a lot of lists like this one or that one that give radicals names, but I could not find one that also has the meaning of the radical.

I got the impression that 四點底, 四點火, 四點兒 were listed more frequently than 四點水 but I could be mistaken.

Interestingly enough, 冫 is often listed as 兩點水兒.

(四點水 does have some google hits)

See the meanings here.

Wikipedia actually does call it 四点火.

Phew. Thanks all, I feel better now.

And next time someone tells me something, even if it is from a native speaker, I promise I'll check first....