This paper examines the audio-visual interaction and perception of water features used over road traffic noise, including their semantic aural properties, as well as their categorization and evocation properties. The research focused on a wide range of small to medium sized water features that can be used in gardens and parks to promote peacefulness and relaxation. Paired comparisons highlighted the inter-dependence between uni-modal (audio-only or visual-only) and bi-modal (audio-visual) perception, indicating that equal attention should be given to the design of both stimuli. In general, natural looking features tended to increase preference scores (compared to audio-only paired comparison scores), while manmade looking features decreased them. Semantic descriptors showed significant correlations with preferences and were found to be more reliable design criteria than physical parameters. A principal component analysis identified three components within the nine semantic attributes tested: "emotional assessment," "sound quality," and "envelopment and temporal variation." The first two showed significant correlations with audio-only preferences, "emotional assessment" being the most important predictor of preferences, and its attributes naturalness, relaxation, and freshness also being significantly correlated with preferences. Categorization results indicated that natural stream sounds are easily identifiable (unlike waterfalls and fountains), while evocation results showed no unique relationship with preferences.