Density is the ratio of mass and volume or we can simply say, density is mass per unit volume. Here, the density of water is given as 1 g/cm^3. To convert it to a different set of units (kg/l), we need to know the relationship between different units of mass and volume. 1 kilogram of a substance contains 1000 grams. Similarly 1 lt of a substance is equal to 1000 cm^3.
That is, 1 kg = 1000 g and 1 l = 1000 cm^3
Therefore, 1 g/cm^3 can also be written as:
`1 g/(cm)^3 xx (1 kg)/(1000 g) xx (1000 cm^3 )/(1 l)`
= 1 kg/l
Thus, the density of water at 4 degree Celsius can be reported to be 1 g/cm^3 or 1 kg/l, both are equivalent to each other.
We can also convert the density of water and other fluids to a number of other units as well.
Hope this helps.