Fair enough about the JEs, which cover it in their みず entries. Given they and the Tanaka sentences aim for the "coming to nothing" sense, I think it should be second. I'll move it up and index the sentences accordingly.

@@ -23 +23,3 @@
-<gloss>something short-lived</gloss>
+<s_inf>oft. as 〜になる</s_inf>
+<gloss>(coming to) nothing</gloss>
+<gloss>naught</gloss>
@@ -29,3 +31 @@
-<s_inf>oft. as 〜になる</s_inf>
-<gloss>(coming to) nothing</gloss>
-<gloss>naught</gloss>
+<gloss>something short-lived</gloss>

Presumably the JEs don't have sense 1 because it's obvious. We tend to lead with the literal meaning unless it's obscure or archaic. Image results for 水の泡 are mostly bubbles.
On second thought, probably didn't need to add "foam" or "froth".

@@ -18,2 +17,0 @@
-<gloss>foam</gloss>
-<gloss>froth</gloss>

However the JEs only have the "(coming to) nothing" sense, and all 7 example sentences are for that sense. Can it be moved to the front? I can reindex, but I think modern usage should take prerence.

daij, meikyo
水の泡	69402	99.1%
水のあわ	646	0.9%

The kokugos have the senses in this order, which I think is better.

@@ -5,0 +6,4 @@
+</k_ele>
+<k_ele>
+<keb>水のあわ</keb>
+<ke_inf>&sK;</ke_inf>
@@ -13,7 +16,0 @@
-<xref type="see" seq="1372070">水泡・2</xref>
-<misc>&id;</misc>
-<gloss>coming to nothing</gloss>
-</sense>
-<sense>
-<pos>&exp;</pos>
-<pos>&n;</pos>
@@ -20,0 +18,2 @@
+<gloss>foam</gloss>
+<gloss>froth</gloss>
@@ -26 +25,9 @@
-<gloss>something that is short-lived</gloss>
+<gloss>something short-lived</gloss>
+</sense>
+<sense>
+<pos>&exp;</pos>
+<pos>&n;</pos>
+<misc>&id;</misc>
+<s_inf>oft. as 〜になる</s_inf>
+<gloss>(coming to) nothing</gloss>
+<gloss>naught</gloss>

Not a useful gloss, IMO.

@@ -27 +26,0 @@
-<gloss>castle made of sand</gloss>