I'm sure this isn't the problem, but if you are watering during midday and it's very hot, the steam created by hot sunlight will damage the plant. If it's too hot, water at night, but if it's normal temps, water in the morning. If it's rainy, you will get mildew if you water at night.

I've made the mistake of watering in midday before and the sun wilted the plants so bad, it took days to become normal. I live in the South where it's hot with much more humidity.

If you have a very good magnifying glass, check the underside of the leaves for spider mites. They are extremely small and difficult to see even with the aid og the magnifying glass. Spider mites killed my squash plants and infested my tomatoes before I realized what it was. It has been extremely hot and dry here in NJ this summer and that made for good conditions for the mites. I have been spraying with all season horticultural oil and rotating with neem oil and it seems I am finally getting the mites in check.

Watering every day is way too much for in ground plants. You've probably rotted the roots. I water every 5-7 days for my in ground plants.

Bacterial wilt, most likely caused by cucumber beetle or squash bug.

"but if you are watering during midday and it's very hot, the steam created by hot sunlight will damage the plant"

very incorrect.

In fact, though it's not the case here...in containers mid-day watering (against conventional logic) helps cool the roots during the heat of the day and helps the plants. On my containers I tend to water at 2-3pm during the worst of the summer heat, especially if they're in darker pots.

Containers dry out too quickly for me and I would imagine on a hot day to water in the morning and at night, but I personally would avoid the midday mark. I've been there. I don't do well in containers and I imagine raised beds are ones that need daily watering too. I agree that maybe it's root rot due to overwatering. Anyone would know better. Most books say to not water every day unless you are nursing young seedlings.