Join the club, gwhext; you are not the only one with hydrangeas stressed out and-or partially dried out. Even at the Dallas Arboretum they are suffering.

Some of those dried out stems may still leaf out so I would just let them be until around mid-May 2012 to see if anything happens. Expect some leaf out from the base when stems dry out. If you just cannot wait to tell if the stems are dried out or not, prune them in 1" or 2" increments but stop either when you get to the bottom or when you hit green. Make sure the shrubs are well mulched, with 3-4" of mulch as this reduces the amount of waterings needed. So instead of watering twice a day say, you may need to water every "X" days instead.

But I think you are watering too much (twice a day). If your soil drains well, that may be ok but otherwise they could develop root rot due to the clay soils so just be careful. Oakleafs will croak if left in wet soil for too long periods but mopheads are more forgiving.

You basically do not need to water if the soil is already moist when you insert a finger into the soil to a depth of 4". If they wilt -as mine do- during the day, that is ok. It is a form of defense mechanism and they usually recover by next morning. Water if you see an extreme looking wilting episode; otherwise check the soil moisture using the finger method. About 1 gallon and half per watering should be enough. When the temps go down and stay down, you can go down to about 1 gallon of water per watering.

If the shrubs are getting sun past 11am or so, consider moving them to a more shaded location or temporarily using shade cloth. You can wait until winter to move them since the plant will then be dormant and it will be less stressful for the plant.

Expect poor bloomage in Spring 2012 as result of all of these problems. Rebloomers may be in better shape; blooms from old wood may be toast but blooms from new wood in late Spring should be fine. Of course, I am assuming we do not go thru another repeat of 2011 next year. And that we get some rain and water rationing does not get worse...

Good luck,
Luis