In the context of the EN’s Commitment to Reuse, does something like the use of the EPA WQX Web Services API for flowing data count?

Yes, the reuse of EPA services such as the EPA WQX Web Services API counts in the context of the EN’s commitment to reuse existing resources. Applicants are encouraged to review the Solicitation Notice’s Evaluation Criteria (see Solicitation Notice Section 6B) and the overview of the project narrative in Appendix E ‘Commitment to Reuse', for more information and guidance.