This is my simple take on a DIY air conditioner. The cooling effect results from water evaporating. In order to increase this effect, I'm using a pump with a mist nozzle and a fan. The pump and the fan are powered by a 12V solar battery, so the system works well off the grid too. For this instructable you will need:

a bucket (a standard sized 5 gallon bucket will do great)
a 12V pump like this one
a 12V fan with a suction cup like this one
a 12V battery
3ft/1m of silicone hose
a micro mist nozzle, I have used this by Gardena

Step 1: Prepare the Bucket

Fill the bucket with tap water.
A gallon/ 5 liter will be enough.

Step 2: Prepare the Pump

Insert the micro nozzle into the silicone hose.
Insert the silicon hose into the outflow of the pump.
Put the pump into the bucket with water.

Step 3: Prepare the Fan

Put the fan inside the bucket.
Moisten the suction cup before putting it on the inside wall of the bucket, so it will stick better.
The fan faces upwards and should be close to the top of the bucket.

Step 4: Wiring

Connect the positive wires of the pump and the fan (red) by twisting.
Connect the negative wires of the pump and the fan (black) by twisting.
Make a final check: Ensure that the pump is under water. The silicone hose should lead to the top of the bucket with the mist nozzle facing downwards into the bucket.
Now you can connect the wires to the 12V battery. Negative to negative (black), positive to positive (red)

Step 5: Finished!

Now your DIY AC should be working! I achieve a temperature reduction of about 25%. Due to its small size this AC is only useful for a single room (e.g. bedroom or small cabin). However it's simple but effective. Enjoy!

PS: If you like this Instructable, please support me in the Water contest. Thanks!