You can set the property values in a fluid container as predefined gradients with values that never change. Because gradients are defined within Maya, no calculations are required at render time making them render more quickly than dynamic grid fluid properties.
A gradient-type fluid property can have a constant value of 1 throughout the container (no gradient), or it can have a gradient of values from 0 to 1 along the X, Y, or Z axis or from the outside of the container to the center of the container. You can scale these values, but otherwise, you cannot change them.
To add gradient contents to a container
Alternatively
If you want a property to behave dynamically, the Contents Method for that property must be defined as Dynamic Grid, notGradient or Static Grid, and the Contents Method for Velocity cannot be Off.