The תנ"ך uses מבול as a (extremely) heavy rain. The translations turned it into a flood.
Just like Renaissance artists made sculptures of Moses with horns because somewhere in the תנ"ך it is written that ראשו של משה קרן or something like that so the Greek translators took the translation of קרן as horn and translated it to "Moses' head grew horns" instead of the right translation in that context that Moses' head shone/glowed/glistened. So the translations from Greek to other European languages kept the wrong translation.
In Hebrew הצפה is used to describe the gathering of standing water like a road or a yard turning into a swimming pool due to heavy rain and poor draining system or when one forgets to turn off the water when the bath is full and the whole bathroom/house is flooded.
In Hebrew שיטפון is used to describe an overflowing river washing everything on its path, like when there is a heavy rain in the desert overfilling dried rivers. In common language it can also be used for the bath example.
I beg to differ with Pumbush and ItaiHadas. מבול is not just "downpour," and "flood" is not a mistranslation. Perhaps it has fallen out of favor in Israel, but the great Reuben Alcalay, who was Chief of the Translation Department of the PM's office in Israel and whose 1965 2-volume dictionary (English- Hebrew, Hebrew-English) was the standard for many years, defined mabul as "flood, deluge (which means flood), inundation." When you look up "flood," the first word given is mabul. הצפה is the fourth choice given. Mabul also came into Yiddish as either flood or very heavy rain.