Not sure why you'd want to cut down on water. A plant needs to be healthy to make seeds, and stressing it by withholding water sure doesn't keep it healthy. Though I guess it's true that a stressed plant is more desperate to make seeds. Stressing a plant in this way will, however, make a plant go to seed prematurely.

Same amount until they start dying back, then you can cut down.

I tend to be more neglectful of plants once they start forming seeds, but I don't ignore them entirely. I keep parsley going a bit longer by nipping off the flower stalk when it begins forming. I grow leaf lettuces, and many of them are still suitable for salads when they're beginning to stretch out before flowering. Some may become too bitter, but I like the bitterness.

Now I know why my grandma made so many wilted lettuce salads with a sweet dressing. The hot dressing neutralizes the bitterness of bolting lettuce.

Annuals and biennials that start to go to seed lose their productivity and focus all their efforts on flowering and setting seed. Unless one is intending to harvest the seed for subsequent use, there is really no reason to maintain the plants any longer. I stop watering and usually just rip them out and plant a fresh crop of whatever ;-))

I should have been more clear. The plants in question have already started going to seed. I was just wondering since they have begun going to seed and I want the dill and parsley to come back next year, if their watering needs at this point changed.

That was my point. If you want the seeds, don't stop watering. The plants need to be healthy to make them. If you want the plants to continue after you've harvested the seed, as noted, don't bother. They're done. Not sure about dill, but parsley is a biennial. The first year is about leaf productivity. The second year is about making seeds. After that, they're done.