In simple cases, the speed of the flow u ≈ ≈ Δ Δ γ γ / μ μ , where Δ Δ γ γ is the difference in surface tension and μ μ is the viscosity of the liquid. Water has a surface tension of around 0.07 N/m, and a viscosity of approximately 10 Pa s, at room temperature. So even variations of a few percent in the surface tension of water can generate Marangoni flows of almost 1 m/s. Thus Marangoni flows are common and easily observed.