There are two ways to get to aguas Blancas, one shorter, the other more "exiting", however in the end you arrive to the same place (just from two different sides). There you then take a road which is not so good, in theory you might make it in normal car, depending if it rained or not. But 4x4 or at least high clearance vehicle with rear traction is better. The last bit of the road is narrow and only one vehicle can go through at a time for quite a long stretch.
Ok, I am posting maps form googleartth wit my GPS track on the map.
You start Constanza and go to Japanese colony, this is straight stretch of asphalted road. Then bitumen ends and you arrive to a more concentrated group of houses/village. You take slight right and keep going up the hill, this is just past the point C14 on the map. The road gets better once it gets out of the village, you get over a small ridge and get into another valley. Here you follow the main road, all the way around the valley until you get to the point 028 on the map. There is a steep turn to the left, this is also a small village. You know that you have missed it if you pass large greenhouses on your right, and the road starts to climb. There is actually a sign there if I am right. Form here the road is narrow and climbs steeply, until you get to point 029, there are the falls. You will be able to see the falls from the road some 100 meters before you get to the "parking lot".
The other way is same up to point C13. Here you turn right and decent down to a creek crossing,(C12) drive throuh a small village (c10) bad road), and then start to climb up into forest. This road is not as good, but it is the road that goes all the way to San Jose de Ocoa via Valle Nuevo. You keep to the main road (keep left), there are some turnoffs now and then ( c08, c09) but it is easy to see which is the main road. After some kilometers you get out of the forest and descent a little, then the road starts to climb again, and there is a intersection before the climb point 028. You have to turn left here, and this road will eventually take you to the point 027. If you arrive to the entrance of Valle Nuevo protected area, that means you have missed the turn at point 27.
Hope it makes sence and helps