A puddle is a small accumulation of liquid, usually water, uncontained on a surface. It can form either in depressions in the surface, or directly upon the flat surface, held together by surface tension. A puddle is generally considered to be small enough to step over or shallow enough to walk through, and too small to traverse with a boat, raft or submarine.

Behaviour

Puddles commonly form during rainstorms, and can cause problems for transport, especially when combined with cold conditions to form patches of ice, which are highly slippery and difficult to see. Due to the angle of the road, puddles tend to be forced by gravity to gather on the edge of the road. This causes the notorious 'splash' as cars drive quickly through the puddle, which causes water to be sprayed onto pedestrians on the adjacent pavement. A puddle on a road is commonly referred to as a Wusher. Sometimes, irresponsible drivers will do this deliberately. Such activity is frowned upon, and in some countries can lead to prosecutions for careless driving [1].

Management

Puddles tend to evaporate quickly due to the high surface area-to-volume ratio, allowing a large number of molecules to be vapourised at once, and as such tend to be short lived. However, due to this property, puddles of chemicals such as bromine, which produce highly toxic vapour, are considered highly dangerous and spills such as this must be dealt with immediately, with emergency evacuation as a common step.

In order to deal with puddles, roads and pavements are often built with a camber (technically called 'crowning'), being slightly convex in nature, to force puddles to drain into the gutter, which has storm drain grates to allow the water to drain into the sewers. In addition to this, some surfaces are made to be porous, allowing the water to drain straight through the surface to the aquifer below.