That's going to assume that your cleric is casting spells at the full speed that they would as if they were in tactical movement. From the movement page;
Tactical movement is used for combat. Characters generally don't walk during combat, for obvious reasons—they hustle or run instead. A character who moves his speed and takes some action is hustling for about half the round and doing something else the other half.
A character can hustle for 1 hour without a problem. Hustling for a second hour in between sleep cycles deals 1 point of nonlethal damage, and each additional hour deals twice the damage taken during the previous hour of hustling. A character who takes any nonlethal damage from hustling becomes fatigued.
A fatigued character can't run or charge and takes a penalty of –2 to Strength and Dexterity. Eliminating the nonlethal damage also eliminates the fatigue.
So, at the very least, I'd round down that amount of created water by a factor of 8, as you can only hustle for around 1 hour a day, not 8. However 1200 Gallons of water is still quite a bit, but your character wouldn't be able to do anything else, (like combat!) that day without becoming fatigued.
Also, from Goods and Services, NPC Spellcasting costs:
Spellcasting Caster level × spell level × 10 gp(3)
(3) See spell description for additional costs. If the additional costs put the spell's total cost above 3,000 gp, that spell is not generally available. Use a spell level of 1/2 for 0-level spells to calculate the cost.
So unless your desert people are willing to spend 5 silver for a gallon of water, it's unlikely they can afford water from the temple. Now, if it's a player that's running the cleric, well, you can't charge the same-rate for your spells. You can do it out of the goodness of your heart, and win the love the of desert people, and that's 'cause you are an adventurer. Welcome to the world where everything's made up, and logical points (sometimes) don't matter!