Titus 3:5
"Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;"
The "washing of regeneration" is the regening of the believer in the cleansing process by the Blood of the Lamb.
The Blood is what washes away sin, with water being the symbol of that washing.
I forgot to add, that washing away of sin by the Blood is in the spirit realm, where our actual salvation takes place in spirit.