A basic question is: How much water to carry? If you hike in fall, winter or spring it's: 3-4 liters/day for each hiker for drinking purposes in the north Dan to Arad, and 5-6 liters/day for each hiker for drinikng from Arad to Eilat. The month of May in Israel for all practical matters is summer, not spring.

If you decide to hike during summer time (May/June to August), well, it is not recommended at all. If you still hike in summer, then more water is required up to 8-9 liters/day may be required for each hiker in the south.

During summer at day time tempertures are really hot 35-45 C / 95-115F and only on the mediterranean shore is a little cooler 29-32C / 85-90F but with 65-75% relative humidity. It takes 3-4 minutes to fry and egg in the desert, using an aluminum plate or just a rock...I mean without any fire...

If you plan properly you need to carry water only for one day. Naturally you'll need to arrange for water drops (caches) before you start the desert section.

It is not recommended to carry water for two days, it's too heavy.

How to arrange a water drop? There are people in the Negev desert who'll take you on a 1 day tour for all water drops in the desert (12 of them).

Share a ride is almost always available. Such a trip costs approx. 1500 shekels (aprox. $400) but if you consider that the ride is shared by 3-4 groups

it means $100-130 for your group for all 12  caches. Usually only one hiker from each group takes the caching trip.

You can find all the details you need about water supply points (SPs) and where to cache water in the desert with specific instructions are  in the guide  .

On the list of trail angels   you can find contact information for people in the desert who will take you on a caching trip. This service is not free of charge.

Enjoy the hike.

Yankale wrote   A basic question is: How much water to carry? If you hike in fall, winter or spring it's: 3-4 liters/day for each hiker for drinking purposes in the north Dan to Arad, and 5-6 liters/day for each hiker for drinikng from Arad to Eilat. The month of May in Israel for all practical matters is summer, not spring. If you decide to hike during summer time (May/June to August), well, it is not recommended at all. If you still hike in summer, then more water is required up to 8-9 liters/day may be required for each hiker in the south.

Question regarding your per day number.  Is it the amount of water you need during the course of the day or per 24 hour period?

In other words if you stop at a water source each evening in the north (where you say 3-4 liters) and you drink 1-2 liters in the evening after arriving during the night and with breakfast...can you leave camp with 2 liters or so.  (Drinking 1-2 liters plus 2 liters = 3-4 in a 24 hour period.)  Or is 3-4 liters the amount you will be drinking between leaving camp and arriving at the next camp? 

North is probably not an issue...actually more concerned with the South (and figuring weights) do you leave camp with 5-6 liters of water or is it okay to start the day with only 4 liters (9 lbs)  or do you need to plan to carry 6 liters (13lbs)

 It is important to note that the heat wave we're experiencing in the last few days are part of the phenomenon known as a "Hamsin":

http://en.wikipedia.org/wiki/Khamsin  

These tend to be only a few days long, and indeed, tonight's weather forecast called for cooler temperatures and more humidity tomorrow.