In the description of the sotah ceremony in Num. 5:18, we read:
The priest shall set the woman before the Lord, and uncover the woman's head, and put the memorial offering in her hands, that being the jealousy offering; and in the priest's hand shall be the bitter water that causes the curse. וְהֶעֱמִיד הַכֹּהֵן אֶת־הָאִשָּׁה לִפְנֵי ה׳ וּפָרַע אֶת־רֹאשׁ הָאִשָּׁה וְנָתַן עַל־כַּפֶּיהָ אֵת מִנְחַת הַזִּכָּרוֹן מִנְחַת קְנָאֹת הִוא וּבְיַד הַכֹּהֵן יִהְיוּ מֵי הַמָּרִים הַמְאָרְרִים׃
In the Samaritan text in place of הַמָּרִים "bitter", it reads המארים. This might be derived from מְאֵרָה, another word for curse, but that would make the phrase a tautology. Another possibility is that it's derived from מָאוֹר and hence means "waters which shed light [on whether the woman is guilty]." Of course, the Samaritans will have a definitive answer, but I don't know what it is.