New Revised Standard Version
On that day a fountain shall be opened for the house of David and the inhabitants of Jerusalem, to cleanse them from sin and impurity.

Contemporary English Version
In the future there will be a fountain, where David's descendants and the people of Jerusalem can wash away their sin and guilt.

New American Bible
On that day a fountain will be opened for the house of David and the inhabitants of Jerusalem, to purify from sin and uncleanness.

Douay-Rheims Bible
In that day there shall be a fountain open to the house of David, and to the inhabitants of Jerusalem: for the washing of the sinner, and of the unclean woman.

In that day there shall be a fountain open to the house of David, and to the inhabitants of Jerusalem: for the washing of the sinner, and of the unclean woman.

that,

Zechariah 12:3,8,11 And it shall come to pass in that day, that I will make Jerusalem a burdensome stone to all people: all that shall lift it up shall be rent and torn, and all the kingdoms of the earth shall be gathered together against her. . . .

a fountain,

Job 9:30,31 If I be washed, as it were, with snow waters, and my hands shall shine ever so clean: . . .

Psalm 51:2,7 Wash me yet more from my iniquity, and cleanse me from my sin. . . .

Isaiah 1:16-18 Wash yourselves, be clean, take away the evil of your devices from my eyes, cease to do perversely, . . .

Ezekiel 36:25 And I will pour upon you clean water, and you shall be cleansed from all your filthiness, and I will cleanse you from all your idols.

John 1:29 The next day, John saw Jesus coming to him; and he saith: Behold the Lamb of God. Behold him who taketh away the sin of the world.

John 19:34,35 But one of the soldiers with a spear opened his side: and immediately there came out blood and water. . . .

1 Corinthians 6:11 And such some of you were. But you are washed: but you are sanctified: but you are justified: in the name of our Lord Jesus Christ and the Spirit of our God.

Ephesians 5:25-27 Husbands, love your wives, as Christ also loved the church and delivered himself up for it: . . .

Titus 3:5-7 Not by the works of justice which we have done, but according to his mercy, he saved us, by the laver of regeneration and renovation of the Holy Ghost. . . .

Hebrews 9:13,14 For if the blood of goats and of oxen, and the ashes of an heifer, being sprinkled, sanctify such as are defiled, to the cleansing of the flesh: . . .

1 John 1:7 But if we walk in the light, as he also is in the light, we have fellowship one with another: And the blood of Jesus Christ his Son cleanseth us from all sin.

1 John 5:6 This is he that came by water and blood, Jesus Christ: not by water only but by water and blood. And it is the Spirit which testifieth that Christ is the truth.

1 Peter 1:19 But with the precious blood of Christ, as of a lamb unspotted and undefiled

Revelation 1:5,6 And from Jesus Christ, who is the faithful witness, the first begotten of the dead and the prince of the kings of the earth, who hath loved us and washed us from our sins in his own blood . . .

Revelation 7:13,14 And one of the ancients answered and said to me: These that are clothed in white robes, who are they? And whence came they? . . .

the house.

Zechariah 12:7,10 And the Lord shall save the tabernacles of Juda, as in the beginning: that the house of David, and the glory of the inhabitants of Jerusalem, may not boast and magnify themselves against Juda. . . .

uncleanness.

Leviticus 15:2-33 Speak to the children of Israel, and say to them: The man that hath an issue of seed, shall be unclean. . . .

Numbers 19:9-22 And a man that is clean shall gather up the ashes of the cow, and shall pour them forth without the camp in a most clean place, that they may be reserved for the multitude of the children of Israel, and for a water of aspersion: because the cow was burnt for sin. . . .

Ezekiel 36:17,29 Son of man, when the house of Israel dwelt in their own land, they defiled it with their ways, and with their doings: their way was before me like the uncleanness of a menstruous woman. . . .