This is one of the few hymns I have written since becoming Catholic. I used it first at Our Lady's Church in Ringwood where I was music coordinator for several years under the admirable Fr Gregory Pritchard (now in charge of the charred St Joseph's at Chelsea).
The tune is a simple folksong ("Parsley sage rosemary and thyme"--made famous by Simon and Garfunkel). John Bell of the Iona Community is really good at doing this sort of thing. It works well, because the tune is dignified and familiar, but is also fresh in that it hasn't been used for a spiritual song before as far as I know.
I wrote a much longer version of this hymn, which draws on the tradition of the seven sacraments flowing from the side of Christ (Catechism 766, 1225), but I never quite got it right. I will post it when I do.
Tune: Scarborough Fair (Hymns Old and New 485)
1. When the spear of sin and pride
forced a wound in Jesus' side,
John saw blood and water flow
from his heart to earth below.
2. Living water, fount of life,
Welling up from deep inside,
Streaming from the throne of the Lamb
Healing every race and land.
3. From his heart flows precious blood,
Filled with life, a saving flood,
Flowing in baptismal streams
Where we wash our garments clean.
© David Schütz
Verse 1: John 19:34 Blood and water from his side, pierced by the spear, wounded by the sin of the world (They shall look upon him whom they have pierced)
Verse 2. Fount of life (John 7:38), Living water, the river of life (Ezekiel 47, Revelation 22:1) flowing from the temple, the city of God, the throne of the lamb, for the healing of the nations.
Verse 3: The elect wash their robes in the blood of Christ and make themselves clean (Rev 7:14) (Rock of Ages: "Foul, I too the fountain fly; wash, me Saviour, or I die.")