I tried to be as faithful to the original melody as possible in making this adaptation.

When adapting a chant melody to fit another language, this is usually not the best approach. In Gregorian Chant, not the melody but the text takes precedence.

You might search for the handouts of a course given by a master of English adaptation of chant, Fr. Columba Kelly OSB. He sets out to look for the structural pitches of a given chant, then analyse the different melodic embellishments as to decide how to apply them to the English text.

I'm no native English speaker, but ‘tem-PLE’ and ‘to whom THIS’ look a bit awkward.

Also, ‘original melody’ can mean quite different things nowadays. In the Graduale Novum you can find a version that might represent the melody from the oldest manuscripts best (see attachment).

Thank you! I would let "whom" cover the next neume, then quarter bar, then put "this" directly after the quarter bar.

Absolutely, I totally agree. I have the Graduale Novum, the Liber Gradualis of Alberto Turco and the work of Anton Stingl. They each make different choices. I should have said "better" instead of "best". But alas, also for the 1903 Graduale Romanun choices were made.

I thought that the extra hyphen was due to the placement of punctuation or a tag, but it's not. It's because the two sets of parentheses are next to each to other without an intervening syllable.

saved(h!iwji)(hvGF)(f.)

That gets the extra hyphen.

saved(h!iwji)hvGFf.) combines everything into one neume, and then you have to deal with "savèd" (not all that weird, but this is what Steven got at earlier.) You could use /manually placed, but since there's no melismatic mora vocis (because there are multiple syllables in the Latin) and because spaces for Mocquereau indicate repercussion but not the mora vocis, this is sort of odd.

I did take out the extra stuff presumably held over from Source and Summit and fixed the typo. You can make use of the Commentary feature for Scriptural elements, the assigned dates of origin, etc. If someone downloads the gabc file, it'll be filled in the file header automatically (Gregobase does some wonderful things, somehow…). The gabc box should start with the clef.

Have been having a hard time improving the melody adaption starting at "whom this water..."

I have attached a photo of an possible solution that begins to take more liberties with the melody, but I'm wondering if it causes more "un-naturalities" than how it was originally.

Not sure if placing the breath mark after "to" or "whom" is optimal. Each requires a sacrifice to be made in the following phrase.

Edit: I'm also wondering if I should add an additional note to end the "-ter" syllable that is the same pitch as the first note of "came". This might improve the flow of the chant in this specific location.

There's also the adaptation by Fr. Samuel Weber, OSB, available here.
It's p. 7 of the PDF (numbered page 327, item no. 1081).

CantorCole, I thought you might be happy to know your setting was chanted today at St. Augustine Cathedral in Kalamazoo (at an episcopal mass, no less).