The ornamental design for a wateranalysisinstrument, as shown and described.
FIG. 1 is a perspective view of the ornamental design for a water analysis instrument.
FIG. 2 is a bottom view thereof.
FIG. 3 is a top view thereof.
FIG. 4 is a left side view thereof.
FIG. 5 is a right side view thereof.
FIG. 6 is a front view thereof; and,
FIG. 7 is a back view thereof.
The broken line showing of structural features is included for the purpose of illustrating non-claimed subject and forms no part of the claimed design.