I recall I used 30C water when mixing xtol. The xtol was fresh, dated 2011 or so. Kodak gives instructions like this:

Start with an amount of water that is approximately
75 percent of the total volume indicated on the
package. See the table above. The water should be at
normal room temperature, about 65 to 85F (18 to
30C).
I'll try glass bottles next time, and maybe even try to get deionized water. My friend hrst said he could probably get the water from some lab at the university.