water route, shipping channel
澪 centers on a marked path through water: a shipping channel or water route that guides vessels safely.
澪 combines 氵 (water) with 零, which likely contributes the sound and may relate to the idea of a defined path or marking. The exact historical development is uncertain.
The water radical 氵 beside 零 (zero) suggests a zero-like path carved through water: a clear, empty channel for ships to follow.
For レイ, imagine a ray of light marking the shipping channel at night: ray -> レイ, guiding boats along the water route.