Yes, the words “water” and “agua” can be counted as two separate words. Researchers recommend assessing young bilingual children’s total vocabulary in both languages for the best indicator of language learning, rather than measuring only concept vocabulary (the number of unique concepts for which a child has words). See Hoff, E., & Core, C. (2015). What Clinicians Need to Know about Bilingual Development. Seminars in Speech and Language, 36, 2 for more information.