If your squash plants are dying like this, even though you are watering them, it's because they have been attacked by squash vine borers.  They dig into the base of the plant's stem and chew it up, killing the plant.  By the time they get into the plant, there's little you can do.

I've had some luck in dowsing the stems with Dipel dust while they are growing and before they get attacked.  There are other remedies, but most people say that few of them are fool proof.

The damage is done by the larva of the squash vine bug, a beautiful creature that somewhat resembles a red wasp.  Here's a picture.

Waiting until later in the season may to plant squash may reduce the possibility of infestation.