We turned our sprinkler system off last weekend so that we could mow the lawn in the morning without the grass being wet. Unfortunately, I forgot to turn the sprinkler system back on and the grass has gotten no water for a week. The grass has large, dry spots where the grass is green/brown. It looks dead but I'm wondering if there's any way to bring it back to life. Any ideas? It's tall fescue (I think) and the weather has been in the high 90s all week.
If you are going to water after a period of stress then you need to keep watering it to keep it green during the summer. Grass has no problems going dormant in the summer but the turf opens up for weeds to get a hold. If you want to keep your lawn to a high percentage of grass and low amount of weeds then it needs to be watered during dry periods otherwise it will go dormant as you have seen.
The other beneficial practice during the summer is to cut the grass high. As high as you can stand. Taller grass can cope better with dry conditions, three inches or more during the summer allows more root growth which, in turn, lets the roots get more water.
Your lawn will be fine. I don't water my (couch) lawns, ever, and they survive weeks and months of 35-40C daytime temperatures in summer without rain, with no ill effects. The grass just stops growing. Fescue is less drought-hardy than couch, but much the same principles apply - my Dad's fescue lawns get watered once a week or once a fortnight, depending on the level of water restrictions we're under.
Water it as per your normal until it recovers - which it will, given time - and then look at reducing your lawns dependence on you, in case this happens again. As others have said, cut the grass higher and slowly reduce the frequency of watering, but I would also look at whether there are drainage improvements to be made, in the long term (if your soil can't hold water, then you have to water daily to keep good-looking lawn).