You need:
acrylic binder / gel
hand-held electric mixer
water and detergent to clean equipment and brushes

Use the electric mixer to work the pigment and water to a thick paste, like toothpaste. Add a roughly equivalent volume of acrylic binder to the water/pigment paste. Mix well with the mixer. The paint can now be used right away.

The paint can be stored but should always be mixed before re-use as the pigment settles down in the binder.