[GTP Dad]

Yes you can check for compression as long as the heads are still on the car. Just be careful not to suck anything in to the engine. If you have to replace the head gaskets make sure you use new bolts. The ones on your car are torque to yield and they must be replaced or you will need to do it all over again.
Did you get water in all cylinders or only a certain one? If there is water in all the cylinders you will probably be doing a headgasket replacement. If only one cylinder makes absolutely certain that you didn't have the gasket slip when you replaced the manifold gasket. If it did then that is probably where the water may be coming from.