The perennial questions about bees nuisance foraging at swimming pools and spas is answered by this new bit of research. The study also shows a potential prevention strategy-- using potassium salt to train bees off a water source.

http://www.ncbi.nlm.nih.gov/pubmed/26823100

J Exp Biol. 2016 Jan 28. pii: jeb.132019. [Epub ahead of print]
Salt preferences of honey bee water foragers.
Lau PW1, Nieh JC2.

Abstract

The importance of dietary salt may explain why bees are often observed collecting brackish water, a habit that may expose them to harmful xenobiotics. However, the individual salt preferences of water-collecting bees were not known. We measured the proboscis extension reflex (PER) response of Apis mellifera water foragers to 0-10% w/w solutions of Na, Mg, and K, which provide essential nutrients,. We also tested phosphate, which can deter foraging. Bees exhibited strong preferences: the most PER responses for 1.5-3% Na and 1.5% Mg. However, K and phosphate were largely aversive and elicited PER responses only for the lowest concentrations, suggesting a way to deter bees from visiting contaminated water. We then analyzed the salt content of water sources that bees collected in urban and semi-urban environments. Bees collected water with a wide range of salt concentrations, but most collected water sources had relatively low salt concentrations, with the exception of seawater and swimming pools, which had >0.6% Na. The high levels of PER responsiveness elicited by 1.5-3% Na may explain why bees are willing to collect such salty water. Interestingly, bees exhibited significant high individual variation in salt preferences: individual identity accounted for 32% of PER responses. Salt specialization may therefore occur in water foragers.