Snowslider is your man for the definitive answer on this - so I'm sure he'll chip in when he reads this. However, I think he'll confirm that you're not going to need a lot of warm clothes!
I don't now about definitive
But it'll be scorchio mostly
Up on the high cols, particularly after a climb, the wind can be fairly chill and if you stay at refugios or huts you'll find the evening can be cool once the sun drops behind the mountain. A fleece and a shell would be enough and I personally in Europe carry a primaloft jacket to sit outside refuges enjoying a beer in the evening.
It's not unheard of that temperatures can drop fairly dramatically at reasonable heights and you'll often feel colder than the temperature might suggest if you're tired and it's been a long day. I was on Corsica last week and it was 30' mostly but we all had fleeces or similar on at some point.
Water consumption varies, 1.5 - 2 litres a day is normal and a couple of nalgene bottles will work best, easier to fill and manage than anything else. Take some water purification tablets so you can fill up on route and pay particular attention to water quality if you're in a water course below a refuge of bivouac site. That's on the trail, you'll see higher daily figure but we're assuming you're getting liquid from food and at breakfast and the end of the day which will bring you up to 4 - 6 litres at least, the trick is to keep "PPP" (pee, plenty and pale)
Otherwise, expect hot days, occasional storms and even more occasional low temperatures or even snow showers
