If your tap water is cool, you can air condition a room with it at minimal cost.

[edit] Steps

Obtain a radiator from a small car such as a Honda Civic, with the electric fan still attached.
Get 50-100' of clear 3/8 to 1/2" PVC tubing, similar to what's used in hospitals, from a hardware store.
Also get all the necessary hose adapters to attach to the radiator and the sink faucet.
Fasten the radiator in some sort of wood or metal enclosure to hold it upright and offer a reasonably aesthetic appearance.
Use a 12-volt power adapter that provides at least 4 amps of power, such as those used to power electric coolers, such as the Koolatron.
Attach it to the wires of the fan, it will run in either direction, pulling air through or pushing it.
Route the tap water from the faucet, through the bottom of the radiator, out the top, and back into the sink. Tape the hoses together for minimal clutter.
You now have an air conditioner.

[edit] Tips

Don't use too much water, just a few liters per minute is usually sufficient.
Close the doors and windows to keep the cool air in.
Compared to a "swamp cooler", this unit has the advantage that it works equally well in humid or dry conditions, whereas a "swamp cooler" only works well in dry conditions. However, this unit uses much more water for a given amount of cooling, so it's only suitable for regions that have plentiful water supply.
This works best in climates that are cold in the winter, where the tap water is the coolest. In the southerns of the northern hemisphere, for example, the water may be too warm to be useful.
Unlike a conventional air conditioner, this unit doesn't need to vent hot air outside.
Try to use the water for something, like the lawn or washing a car.

If your water is metered, calculate how much you are using, and keep it within your budget. Well water is usually quite cool, but keep an eye on the pumping costs.
This unit can be a bit noisy, so it could be built with some soundproofing, or ducted from another room.
In areas with limited water supply, using water this way is irresponsible, whether it is metered and you pay for it or not.
Many well pumps are not rated at 100% duty cycle. Be careful leaving this running on a well pump.
You could run your well dry and burn up the well pump.
Water that has passed through a used radiator would likely be unsafe for human and animal needs.