Incidentally, not that you'll listen, but here's Hoehner's take on it:
"Many think this refers to baptism. Unfortunately, this is reading patristic and modern liturgy into the first century, and moreover, there is nothing in the present context or in
Titus 3:5 to indicate that this has reference to a baptismal rite. Furthermore, the rite of baptism does not cleanse one from sin. Even in the Qumran community the ritual washing was not considered as that which cleansed them. Rather, it was God who wiped out their transgressions and justified them. Also, as Erdmann rightly observes, nowhere in the NT is the rite of baptism used in connection with the entire Christian community but only in connection with individual believers. On the other hand, Barth and Dunn think it is a reference to the baptism of the Spirit. Once again, nothing in the present context suggests the Spirit's baptism.
It is probably best to see it as a metaphorical expression of redemption with the imagery of the bridal bath practiced in the first century. Christ gave himself for the community of believers, the church. The purpose of this was to set apart the church because she had been cleaned with the washing of water. In
1 Corinthians 6:11 it also mentions washing. There, unlike those who will not inherit the kingdom of God, believers were washed, sanctified, and justified in the name of the Lord Jesus Christ and in the Spirit of God. Here, too, the washing has reference to the cleansing accomplished by Christ and not the ritual of baptism. In
Titus 3:5 it refers to the washing of regeneration, indicating a cleansing that comes with salvation making us acceptable before a Holy God. Why is the term "water" used? The most likely explanation is that water is the most common element used for washing. Along with the above mentioned,
Hebrews 10:22 refers to the new covenant that promises forgiveness of sin as fulfilled by Jesus' death allowing those who trust in that death to come to God because their hearts were sprinkled clean from an evil conscience and their bodies washed with pure water. Again, these are picturesque ways of expressing the cleansing affected by Christ's death. None of these passages have any suggestion of a sacramental setting. Nothing appears to be part of a formula associated with baptism such as "in the name of Jesus" or "in the name of the Father, Son, and the Holy Spirit." Furthermore, the idea of washing involves bathing rather than just a few drops of water or a quick dip into the water. In addition, baptism is always administered individually whereas this context speaks of the effect of Christ's death on the body of believers. As initially stated then, the washing of water is a metaphorical way to express cleansing.
As mentioned above, not only is this a metaphorical expression of redemption, but it also evokes the imagery of the bridal bath. This is significant since the present passage deals with the relationship of the husband to his wife. The prenuptial bath in Jewish marital customs reflected the imagery of God's marriage to Israel related in Ezekiel 16. At the time of her birth, Israel was in a pitiable state, lying in blood, uncleansed by the washing of water, and was abhorred by all (16:4-6). When she grew up God entered into a covenant with her and bathed her with water, washed off the blood, anointed her with oil, and clothed her with the finest materials, making her exceedingly beautiful, fit to be a queen (16:8-14). The custom of prenuptial bathing seemed to be practiced also among the Greeks. Analogous to this bridal bath, the present verse relates that Christ's death on behalf of the church was to cleanse her by the "washing of the water."
(Harold W. Hoehner, "Ephesians: An Exegetical Commentary", pp. 753-754)