Conventional water chemistry parameters such as hardness, alkalinity, and organic carbon are known to affect the acutely lethal toxicity of copper to fish and other aquatic organisms. In the present study, we investigate the influence of these water chemistry parameters on short-term (3 h), sublethal (0-40 microg/L) copper toxicity to the peripheral mechanosensory system of larval zebrafish (Danio rerio) using an in vivo fluorescent marker of lateral line sensory neuron (hair cell) integrity. We studied the influence of hardness (via CaCl2, MgSO4, or both at a 2:1 molar ratio), sodium (via NaHCO3 or NaCl), and organic carbon on copper-induced neurotoxicity to zebrafish lateral line neurons over a range of environmentally relevant water chemistries. For all water parameters but organic carbon, the reductions in copper toxicity, although statistically significant, were small. Increasing organic carbon across a range of environmentally relevant concentrations (0.1-4.3 mg/L) increased the EC50 for copper toxicity (the effective concentration resulting in a 50% loss of hair cells) from approximately 12 microg/L to approximately 50 microg/L. Finally, we used an ionoregulatory-based biotic ligand model to compare copper toxicity mediated by targets in the fish gill and lateral line. Relative to copper toxicity via the gill, we find that individual water chemistry parameters are less influential in terms of reducing cytotoxic impacts to the mechanosensory system.