The clear portion of this separator bowl is water that's been centrifuged out of the fuel.
This large cartridge-type particulate filter from a Racor separator was designed to trap dirt and grit, not water. It must be changed periodically.
Getting to the cartridge to change it is easy-as long as you have good access.
The T-handle should be only hand-tight, so you shouldn't need a wrench.
Removing the old cartridge is relatively easy thanks to the integral plastic handle, which folds flat when the cartridge is actually in place.
You may need to pry it up with a screwdriver so you can grab it. The filter will come out saturated with diesel fuel, so make sure you have plenty of absorbent pads handy.
The most important part of changing the cartridge is making sure the unit is completely full of fuel.
Any space will allow air to enter the fuel system.