Let's take a look at a strange Midrash that comments/expands upon the text of the first plague in the Book of Exodus:
and the fish in the Nile will die. The Nile will stink so that the Egyptians will find it impossible to drink the water of the Nile.’”
(י) וְהַדָּגָה אֲשֶׁר בַּיְאֹר מֵתָה, אָמַר רַבִּי אָבִין הַלֵּוִי בְּרַבִּי, מִמַּכַּת דָּם הֶעֱשִׁירוּ יִשְׂרָאֵל, כֵּיצַד?
הַמִּצְרִי וְיִשְׂרָאֵל בְּבַיִת אֶחָד וְהַגִּיגִית מְלֵאָה מַיִם, וּמִצְרִי הָלַךְ לְמַלְאוֹת הַקִּיתוֹן מִתּוֹכָהּ מוֹצִיאָהּ מְלֵאָה דָּם, וְיִשְׂרָאֵל שׁוֹתֶה מַיִם מִתּוֹךְ הַגִּיגִית, וְהַמִּצְרִי אוֹמֵר תֵּן לִי בְּיָדְךָ מְעַט מַיִם וְנוֹתֵן לוֹ וְנַעֲשׂוּ דָּם, וְאוֹמֵר לוֹ נִשְׁתֶּה אֲנִי וְאַתָּה מִן קְעָרָה אַחַת, וְיִשְׂרָאֵל שׁוֹתֶה מַיִם וְהַמִּצְרִי דָּם, וּכְשֶׁהָיָה לוֹקֵחַ מִיִּשְׂרָאֵל בְּדָמִים, הָיָה שׁוֹתֶה מַיִם, מִכָּאן הֶעֱשִׁירוּ יִשְׂרָאֵל.
...and the fish in the Nile died...
Said Rabbi Avin HaLevi son of Rabbi:
"The Israelites grew wealthy via the Plague of Blood."
How was that?!?
If an Egyptian and a Jew were in one house, with a (single) tub filled with water. When the Egyptian went to fill their cup from the tub, they would end up with a cup full of blood, while the Israelite would drink water from the same tank.
If the Egyptian said to the Israelite, "give me some of your water." (As soon as) the Israelite gave it to the Egyptian, it would become blood.
If the Egyptian said to the Israelite, "let's both drink from one cup," the Israelite would drink water, while the Egyptian would drink blood.
But, when the Egyptian would purchase the water from the Israelite, they would then drink water.
From this episodes, the Israelites became wealthy.