Limpid

limpid \ˈlim-pəd\ adjective: 1 a. marked by transparency; pellucid {limpid streams}, b. clear and simple in style {limpid prose},
2. absolutely serene and untroubled

Etymology: French limpide, from Latin limpidus, perhaps from lympha water

Compare limpid to diaphanous, pellucid, transpicuous and perspicuous.