How do plants actually drink, and why does a plant wilt?

Water is not pumped — it is pulled up the plant by evaporation from the leaves, and wilting is what happens when that pull outruns the supply.

The mechanism, working from the top down:

Transpiration. Water evaporates from the moist internal surfaces of leaves and escapes through pores called stomata. This is the engine, and it is passive — the sun supplies the energy.

Cohesion and tension. Water molecules stick strongly to one another through hydrogen bonding. As one molecule leaves the leaf, it drags the next along behind it, creating a continuous column of water under tension running from leaf to root. The column in the xylem — a chain of hollow dead cells forming pipes — is effectively pulled from above, not pushed from below.

Root uptake. Water enters root hairs by osmosis, following the tension already created above.

Why this is remarkable. A tall tree lifts water over a hundred metres with no moving parts and no energy expenditure of its own. It works because the water column can sustain enormous tension without breaking, provided it is not interrupted.

What wilting actually is. Plant cells are held rigid by turgor — internal water pressure pushing the cell contents against the cell wall, like air in a tyre. Lose water faster than it is replaced and turgor falls, cells go slack, and leaves and soft stems droop. It is a structural failure of pressure, not damage.

Why wilting is sometimes protective. A plant wilting in midday heat may be transpiring faster than the roots can supply, even in moist soil, and recovers by evening. Watering a plant that is wilting from heat rather than drought can drown it. Check the soil, not the leaves.

Why overwatering causes the same look. Waterlogged soil has no air, roots suffocate and die, and a plant with dead roots cannot take up water — so it wilts while standing in it.

Why stomata close in heat — to conserve water at the cost of pausing photosynthesis.