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Osmosis is a Spontaneous Process.

Water moves down a chemical-potential gradient (water potential) from a region of high water potential to an area of low water potential.

Pure Water has the Highest Water Potential which is set at ZERO.

Water Potential is influenced by Concentration, Pressure & Gravity

Solutes

Solute Potential (a.k.a. Osmotic Potential) represents the effects of solutes on Water Potential.

Solutes lower the water potential by diluting the water molecules.
Since water is often used to dilute solutions, you need to reverse your perspective to understand how water is diluted by Solutes dissolved in it.

The addition of a Solute increases Entropy, and thus reduces the Potential Energy of Water. The addition of a Solute Decreases Water Potential.

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Pure Water has Low Entropy

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Water Diluted by a Solute (Red Spheres) has higher Entropy than Pure Water. It thus has less Water Potential
A simple way to demonstrate Osmosis is to place a semi-permeable membrane over a funnel that contains an impermeable solute solution inside. The membrane is permeable to water but impermeable to the solute. This is placed in a beaker of Pure Water. Pure water has the highest Water Potential. The solution inside the funnel has a comparatively low Water Potential. Osmometer-1-500.jpg (76267 bytes)

Water molecules will move from an area of high concentration to one of low concentration. Consequently, they will move across the membrane while the solute molecules can not. This will increase the Volume inside the funnel. This produces a Pressure that will push the solution up the stem of the funnel. If a pressure gauge is placed at the tip of the funnel the pressure could be measured.

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