Although the phrase with water (instrument) may be rendered “in water” (location), the former meaning seems intended in light of the parallel in verse 33 (with the Holy Spirit). All modern translations have with water.

I baptize with water must be rendered in some languages “I baptize people with water.” In other languages a special habitual form of the verb is required, for example, “I habitually baptize people with water” or “It is my custom to baptize people with water.”

In the clause you do not know, the pronoun you is emphatic. This statement must not necessarily be taken to imply that none of the people there knew Jesus, but rather that they did not recognize him for who he was. In some languages it may be useful to translate know as “recognize,” and even in a somewhat expanded form, “you do not recognize him for who he is.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .