Watering the Lawn

The most popular housing in America is the suburban house. It's close enough to the city to have a reasonably short commute for work, shopping, or emergency assistance, but far away enough to be reasonably priced and to offer considerable privacy from one's neighbors.
Almost all houses are surrounded by a grass lawn, which is nice to walk or play on and looks reasonably good too. But the lawn gets thirsty, and must be watered, or it will die. Thankfully, all houses also come with a water system, which pretty much always has a nozzle outside to work with. We have many options.

* Hose
A flexible tube of rubber-like material bought in any hardware store. Connects to outside faucet, and is able to deliver water around the yard.
+ No extra infrastructure required
+ Cheap
- Not Automatic
- Slow
- Requires your personal presence, even on really hot days
- Very high evaporation losses

* Sprinkler system
A series of pipes is dug in the yard, leading to sprinkler heads. The heads spray the water about, and if well positioned, are able to water everything. Larger yards may require several "circuits," as water pressure is limited.
+ Waters entire yard
+ Can be automated if a timer and rain sensor is added
+ Can be operated from indoors on hot days
- Extensive digging required
- Timer and rain sensors expensive
- Sprinkler heads can be damaged by mowing
- High evaporation losses

* Drip system
Black hoses with little holes in them are distributed through the yard. When water is run through the black hoses, it gently leaks out the hose and into the grass.
+ Waters entire yard
+ Can be automated if a timer and rain sensor is added
+ Can be operated from indoors on hot days
+ Lower evaporation losses
- Timer and rain sensors expensive
- Hoses easily damaged by mowing or animals, and difficult to repair
- Costs more than hose or sprinkler system

* Underground drip pipe
Pipes with holes in them are laid in trenches and covered. The pipes lead to an open pipe on the surface, above which a water spigot is able to introduce water to the system. The system waters the lawn from beneath. This is the system that I personally endorse.

+ Waters entire yard
+ Can be automated if a timer and rain sensor is added
+ Can be operated from indoors on hot days
+ Smallest evaporation losses
+ Encourages deep roots
- Absurd amount of digging and plumbing work required
- Timer and rain sensors expensive
- Most expensive option
- Plants will try to insert their roots into the pipes to monopolize the water supply

* Watering Blimp
A helium balloon suspends a water tank above the yard. A small fan is able to propel the system about, and a small inboard computer such as an Arduino tracks GPS coordinates and notes what spots are watered and what spots need more watering. A nozzle in the tank allows it to water the sections that it's floating over. When the tank is empty, it can return to a predetermined spot for you to refill it. Tank should be large enough for at least one day's worth of watering, because I really don't want to spend my day running over to refill the damn thing. Also, must have knowledge of the GPS coordinates of your property lines, otherwise it would water your neighbor's lawns too at your expense.
+ Hillarious
+ Major conversation piece
+ Waters entire yard with no intervention after initial setup
- Needs hose refilling
- Excessively crazy
- Very high evaporation losses
- Hard to set up. (Do YOU know the GPS coordinates of your property lines?)

* Weather Control
Using some as yet of undetermined means, control the weather such that your lawn receives exactly as much rain as it needs. Preferably in the pre-dawn morning so that it doesn't inconvenience you personally.
+ Automatic
+ Free after setup
+ No wasted water, ever
+ Much easier on city utility system
- Not sure how you're going to do this, chief.
- Possible detrimental effect on rest of ecosystem
- Almost assuredly extremely expensive to set up
- Excessively crazy

Farms can also use any of these systems to water the crops, and most of them seem to prefer the sprinkler technique, using a very large framework of mobile pipes and a very long hose.