Water. It's predicted that the system, assuming no leaks, will use approx 2 gal of water every 5 hours. (I'll revise this later as I confirm with testing) So an extra 2 gal per day should get you through the hottest part of the day. Best to start the cooler before things heat up too much inside... it's easier to maintain cool inside temps than lower high temps.
Regarding Power:
You need a 12v power source, size depends on how long you want to run it and what size fan and pump you use. I'm using the 115amp-hour Deep Cycle Marine Battery from Costco (~$80). This is handy for powering all sorts of things, of course, not just the swamp cooler! Depending on how much you run the cooler (and how many other things you run), you may need a way to recharge this battery at some point during the week. Make friends with someone who has a generator, or hook it up to your car with jumper cables and run the engine for 20 minutes or so.
The whole thing CAN run on solar power if desired. A 10-15w panel will push fans like mine directly (1.2amp total draw), or via a deep cycle marine battery, and the pump can either be solar or also run from a small panel (10w panel for the silicon solar pump alone) or the battery. Bigger fans and bigger pumps may need more juice. eBay has tons of panels on sale for some reasonable prices, but bear in mind if you start getting too elaborate you may need charge controllers, etc. which will drive up the price and complexity. Simplest is to just run off the included solar (for the pump) and run the fans off a battery or 10-15w panel, directly, or run off the battery directly and recharge as needed.
Easiest way to physically connect the various power components is to use simple cigarette power plugs and a cigarette lighter-style socket. Sockets with a pair of battery clamps on the other end are easily available at Pep Boys, RV/Camper stores, Radio Shack (not the cheapest option) online, etc. I bought a replacement plug at Radio Shack with an 8' cord on it, snipped off the end, and connected the two power wires (black-neg, and black with stripe-pos) to the two power wires coming out of the fan connector (black is always negative, red is positive). Solder them together for the best connection, protect with shrink-wrap. A friend can probably help with this if you've never soldered before, but soldering two simple wires together is VERY simple, even a beginner can do this. Or ask a friend. :) Once all the items have easy cigarette plugs on the end, a splitter from Pep Boys (about $5) gives you all the power ports you need.
REGARDING BATTERIES:
If you have ready access to recharging facilities or only short-term use, deep cycle marine batteries are a great power to power this rig. (Regular car batteries, non-deep cycle, are NOT a great idea for a variety of reasons I won't waste space going into.) Here are a few notes regarding their use:
The key number you will be dealing with is "amperage". Batteries are rated with the number of amps they can put out for an hour (although they generally can't actually do it all at once) Look at the amp-hour rating of the battery, it'll be right on the label. (For instance, the Costco deep cycle marine battery is 115 amp-hours) Deep cycle batteries are designed to be taken down to HALF of their rated capacity before recharging. Lower than half and you start to physically damage the battery, as it eats it's own inner workings to try to continue supplying power. This means the Costco battery delivers 57.5 usable amp-hours of power.
Now take a look at your devices, and how much power they draw. The two fans I have recommended, the Scythe Kaze Ultras, use 0.6 amps each, so 1.2 amps to run the fans. It's easy to see that the Costco battery will run these fans for a little over 47 hours before giving out. If you're at an event like Burning Man for the full 7 days, you can run the fans (only) for a little over 6 1/2 hours per day before you'll need to recharge the battery. If you have the Silicon Solar fountain pump, which draws 300 milliamps (0.3 amps), add in that power, so 1.5 amps, and you can see you can run the combo for just over 38 hours, or just under 5 1/2 hours per day over 7 days. If you're running anything else off the battery, it won't last as long. That's your general theory, now you just need to add up all the numbers!
These numbers are all theoretical... real world usage often reflects less-than-ideal results, so be sure to pad your numbers and don't try to run things to the wire!
BUILD INSTRUCTIONS:
Photo Diary: DIY Bucket Swamp Cooler Construction
There are a number of screens of photos so be sure to click to the next page each time!
Full credit to FigJam for adapting this original playa-tested design to the small 5 gal. form factor.
Full text instructions:
1) Buy the stuff
2) Add 2 gallons of water to the bucket to establish a high water mark. Use a sharpie to draw a line around the outside. (I drew one line at 1 gal, and another at 2. It made me happy.) Keeping about 1" above that fill line, and below the top reinforcement ring that's about 2" below the top, drill as many holes into the bucket as you reasonably can, using a 2" hole drill bit to allow air to pass through, while still leaving it structurally viable!
3) Cut the shade cloth to a 13" x 6' strip with scissors. This will roll up in a tube, covering the inside of the bucket and acting as an air filter. The 6' length will give you, essentially, a double-layer filter inside.
4) Cut the swamp cooler pad with scissors to 13" x 30". Coil it inside the bucket, and trim as needed to it fits nicely. You'll want to cut a slight wedge off one side since the bucket is a little smaller at the bottom than at the top. About 1" off at the bottom, angled towards the top edge, should give it just the right slight cone shape.
5) Cut about 4' of irrigation tubing off to work with. Cuts pretty easily by slicing as if it were cheese, using a simple box cutter. Use the T-coupler to make a coil that just fits inside the top of the bucket, about 1" down from the edge of the top. The rest of the 4' section will go from the center exit of the T-coupler toward the bottom of the bucket... it should slide right over the output of the fountain pump.
6) Put the fountain in the bottom of the bucket and make sure the tube leading down from the irrigation tube ring is the right length. Trim as needed. Route the power cable for the fountain behind the shade cloth and out one of the big air holes we drilled in step 2.
7) Using a small drill bit (1/16" is about right), drill holes roughly every 2" in the bottom of the irrigation tube ring (no need for precision, it doesn't matter). This will allow water to squirt down onto the cooler pad, keeping it wet, so the evaporation take place properly. NOT the tube going down to the pump, of course, just the ring itself.
8) Now we turn to the computer fans. Place a fan on the bucket lid, right against the edge but inside the top "ring"/ridge around the edge. You do need to be right against the edge or you won't be able to fit both fans side-by-side across the lid. Using a small drill bit or even a thin pen, mark the four holes at each corner of the fan. Use a drill bit that fits comfortably inside the fan's mounting holes to drill starter holes. (Not too big, not too small) I think I used a 1/8" drill bit. I didn't even use a drill, the plastic is very soft. By starting the holes with a 1/16" bit, I easily hand-twisted the bit right through the plastic, checked with the fan to make sure everything lined up right on all four holes, then enlarged the holes with the bigger drill bit, again, just by twisting the bare bit in the hole, by hand.
9) Now we cut the hole in the lid for the fan. Hold the fan in place so you can see the holes are in the right place. Take a pen or sharpie and draw a rough square, well-inside the fan's circular fan part. Make sure it's not too big and you have plenty of "corner" left for the screw holes to stay in place. Now take a standard box cutter knife (Stanley utility knife) and just cut the soft plastic square out. Check with the fan placement again, and using the knife, carefully enlarge the hole by carving out the soft plastic until you have a hole just big enough to have a clear air passage, and still have plenty of plastic at the corners to hold the fan. Be especially careful along the edge that's in the middle of the lid... you need an intact strip of plastic between the two fans to keep the lid structurally strong.
10) Once you've cut the hole and you're happy with it, mount the fan into the lid. (The fans come with screw for this) They screw from the bottom of the lid into the lower corner hole of the fan.
11) Repeat for fan #2. Again, make sure there is an intact strip between the two fans to keep the lid intact.
12) Add 2 gallons of water, connect the fans and pump to power (or hook up the solar panels and take everything into direct sunlight) and watch it go! Make sure there are no leaks. You may want a planter dish from a nursery to catch any drippings from the bucket. Fine-tune the position of the holes drilled into the poly irrigation line if needed... it shouldn't be a big deal to cut a new ring if needed, the stuff is cheap after all, and coming in 50' quantities, you have lots!
13) Use ducting of some sort to route air from the fans to your yurt or other temporary domicile. Attach with silicon sealant, or get creative! (Photos of some ideas to come)
14) Enjoy! Remember, swamp coolers are only effective in climates with very low humidity.
If you have any questions, feel free to drop me a line. :-)