Answer is: 1 mL or 1 cm³.
V(water) = 1 L; volume of the water.
One liter is equal to 1000 milliliters (mL) or 1000 cubic centimetres (1000 cm³).
V(water) = 1 L · 1000 mL/L.
V(water) = 1000 mL.
V(cube) = 1000 mL ÷ 1000.
V(cube) = 1 mL; volume of the cube.