Here's why:

* Viscosity: Resistance to flow is primarily determined by a liquid's viscosity. Water has a very low viscosity, meaning its molecules flow easily past each other.

* Other factors: While viscosity is the primary factor, other things like temperature and the presence of dissolved substances can affect a liquid's flow resistance.

Note: While water has a low viscosity compared to many other liquids, it's important to remember that there are liquids with even lower viscosities, such as some types of oils and solvents.