"Watermark" received generally positive reviews from critics. In an April 1988 review, "Hot Press" reporter Liam Fay wrote the album is "A lifetime's worth of sights, sounds and experiences condescend into an orderly and lucid aural aquarium". He praised her orchestral-like vocals on "Cursum Perficio", the instrumentation on "Storms in Africa", "The Longships", and "Exile", and the "exquisite liqueous pop" of "Orinoco Flow" which, as he predicted, "should be a hit single". Fay was aware that lyrics in such types of music can be the weak point, but deemed Roma's lyrics are "integral and are ideally sculpted to allow Enya's voice to float between the gaps and pauses". Fay also felt "Na Laetha Geal M'óige", "On Your Shore", and "Evening Falls..." sound "too hymn-like for their own good", and pale in comparison to the rest of the album and Ryan's production "reveals a different hue" each time one listens to it. Joe Brown praised it in "The Washington Post", calling it "a lovely collection of quasi-mystical pop" that is "somewhere outside of the pop mainstream but steering clear of the sugary shoals of New Age". He described "Orinoco Flow" as "lushly romantic" and praised the production on "Evening Falls..." and "Miss Clare Remembers", which evoke a "cathedral ambience, with multitracked choirs and shimmering echo".