Rabbi Elazar explains that the place of Marah was a test for the children of Israel. Because there were people suspecting that their wives were with Egyptians and the Egyptians claimed to have many of them among the Israelites, God brought them to the bitter waters in Marah to test them as the priest tests the unfaithful woman.
“וַיִּצְעַק אֶל יְהוָה וַיּוֹרֵהוּ יְהוָה עֵץ וַיַּשְׁלֵךְ אֶל הַמַּיִם וַיִּמְתְּקוּ הַמָּיִם שָׁם שָׂם לוֹ חֹק וּמִשְׁפָּט וְשָׁם נִסָּהוּ.”
Moses cried to God that answered him that because of the judgment of the Egyptians, he is testing the women of the Israelites. God asked him to write the holy name and throw it into the water so everyone will be tested and remove the judgment before he restores his blessings upon them.
The verse that follows reveals the blessing that God can bestow on us when we follow him.
“וַיֹּאמֶר אִם-שָׁמוֹעַ תִּשְׁמַע לְקוֹל יְהוָה אֱלֹהֶיךָ, וְהַיָּשָׁר בְּעֵינָיו תַּעֲשֶׂה, וְהַאֲזַנְתָּ לְמִצְוֺתָיו, וְשָׁמַרְתָּ כָּל-חֻקָּיו–כָּל-הַמַּחֲלָה אֲשֶׁר-שַׂמְתִּי בְמִצְרַיִם, לֹא-אָשִׂים עָלֶיךָ, כִּי אֲנִי יְהוָה, רֹפְאֶךָ.”
“And He said, “If you will give earnest heed to the voice of YHVH your God, and do what is right in His sight, and give ear to His commandments, and keep all His statutes, I will put none of the diseases on you which I have put on the Egyptians; for I, YHVH, am your healer.”
#68 (not in the text above)
Even though the Israelites were many years in Egypt and had many opportunities to sin with the Egyptians, men and women were tested in Marah and they came clean. The process was made to remove doubts that Egyptian seeds grew among them. The test was with water because the holy name can be easily transferred through water.
The soul is a spark of the YHVH name. It is holy and connects to the fetus body through water 40 days after inception. A Mikveh has a measure of 40 seah. Moses stayed 40 days and night on mount Sinai to receive the Holy Torah, that is the aspect of living water.
A purified/distilled water with nothing but simple H2O (not even minerals) is a better conduit for the light and life force.