Depending on the type, poly urethane has strong resistance to the effects of water ingress and has excellent long-term stability in water up to 50 degrees. It is recommended to avoid continuous use in hot water above 80 degrees.
It has very low water absorption, and it weighs -- in the range of 0.3 to 1 percent, there's very little volume expansion. This can be said to be possible, for example, within the margin of error, in a bearing system used as a lubricant for water by a forelethan.
Elastomer has a relatively high water spray transfer rate, and in some cases, this is a solvent benefit. However, if these characteristics are disadvantageous, you should consult the Technical Service regarding the applicability of the elastomer.