What are the origins of baptism:

The tradition of Baptism comes from the old Jewish practice of washing one’s self before entering the temple.

[Moses] placed the basin between the Tent of Meeting and the altar and put water in it for washing, and Moses and Aaron and his sons used it to wash their hands and feet. They washed whenever they entered the Tent of Meeting or approached the altar, as the LORD commanded Moses.

Exodus 40:30-32

The word wash appears 36 times in the book of Leviticus (book regulating religious practices). This practice of washing prepared one to make a burnt offering to God. While the act of washing did not cleanse you of sins, it did make you “ceremonially clean” and able to have your sins forgiven through sacrifice.

Initially, basins were set up outside the Tent of Meeting (early manifestation of what would become the Jewish Temple). In these basins, one would wash only their feet and hands in preparation to worship God. This practice remained up to the time of Jesus. While full body submersion was not necessary, it was not uncommon.

At the building of the first Temple, a large basin (called the Sea of Solomon) which held over 11,000 gallons (42 kiloliters) of water was constructed:

He made the Sea of cast metal, circular in shape, measuring ten cubits 5 feet or 4.5 meters] from rim to rim and five cubits high. It took a line of thirty cubits to measure around it. Below the rim, grounds encircled it – ten to a cubit, the grounds were cast in two rows in one piece with the Sea.

1 Kings 7:23-24