Zion early September

A gear list with weights would help so we can help you evaluate how to lower your weight otherwise it will be difficult.
Suggested GEAR LIST ETIQUETTE
STEVEN EVAN’S 2010 TRANS ZION TRAVERSE TRIP REPORT
STEVEN EVAN’S GEAR LIST FOR THE TRIP
STEVEN EVAN’S VIDEO TRIP REPORT
ANDREW SKURKA’S Maps, Databook & More Info The Databook is a barebones spreadsheet of key information and distances between them. It’s very helpful in quickly determining how miles you’ve covered, how many miles you have left, how many miles to the next water source, etc. The mileage information is on the maps too but the maps cannot be as quickly referenced.There are other links on his site with more info

Not specific to Zion but,
Here is some general info for you to look at
Mike Clelland(NOLs instructor and author, his books are very good),he has some great FREE VIDEOS on lightening up be sure to watch(his clothing system,the entire contents of his pack,water treatment and part 1 and 2 on the dinky stuff for ideas),this is a simple SPREAD SHEET for you to download,this is pmags Lightweight Backpacking 101 and The Frugal Backpacker – The $300 Gear Challenge .These are some other articles and videos for you to check out

Backpacking for Cheap: Gear for the Gearless

Backpacking Checklist (Gear List): 3-Season, 3-Day

Lightweight Backpacking 101: An Introductory Manual for Lightening Your Load Today (1st Edition – August 2001)

Cheap Ultralight Gear List

Oregon Field Guide: Ultralight Hiking

Lightweight Testimony: Lighter, Farther, Faster
Jamie Shortt talks about his progression and shows his gear list for each stage, Lightweight Testimony: My Journey into Lightweight Backpacking
CleverHiker Light weight Basics
CleverHiker Trail Skills
NICK GATEL’S 61st Birthday Trip Report with gear list and discussion

Andrew Skurka has a very good website with trips and gear lists for you to check out, here is a talk he gave at google
Ultimate Hiking Gear & Skills Clinic
His book is worth checking out also
The Ultimate Hiker’s Gear Guide: Tools & Techniques to Hit the Trail
You can get little repackaging containers(like the ones you see in Mike Clelland uses in his videos) many places including your local stores and pharmacy but here are some examples
USPLASTICS
USPLASTICS
Ultralight Designs
GossamerGear
MountainLaurelDesigns
You could make toothpaste dots like Mike C. shows or there are Archtek Toothpaste Tablets so only bring exactly what you need in a snack size bag for any given trip instead of a whole tube and THESE are good for little thing like pills, toothpaste tablets ect. so you are not packing a whole bottle(you can also get them very cheap at most pharmacies) .

– do I need a full tent with mosquito net ? Are there bugs and mosquitoes ? I have a MSR Elixir 3 persons anyone knows if possible to use only the rain fly ?

Very few bugs, I personally would not bring a bug net of any kind.

– how much water should We carry ?

Depends on the weather; early September could still be very warm. I'd want the ability to do six liters a person just in case.

Even in April, it was crucial that I had a gallon of water cached at the wildcat canyon trailhead area. There was water in hop valley, but I definitely wouldn't want to drink it. Also had to rely on a few specific springs that had some water at that time, but I have no idea if they continue to flow in September.

Jean-Claude: I tried to send you a PM, but your email is not set up yet. Please set it up so we can chat. Thanks!