All terraces in a subak are connected to one canal and therefore have one source of water to share. Water can be redirected easily by putting blocks in entrances to some fields and opening others. The blockings and openings and amounts of time given for the distribution are all decided upon by voting that must conclude with a unanimous decision. It would be easy for a farmer to redirect the water without being noticed by the other farmers briefly by placing a stone barrier in the way.
Cheating the unanimous decisions is so rare that when asked about the problem of cheating, Professor Wyan Windia, our guide and mentor in our first subak, had a difficult time directly answering the question. So, why is cheating the system so extremely rare?
Professor Wayan tells us that the gods are always watching the farmers. Even if they are not caught by other farmers, bad karma comes if anyone goes against the decision of the group. However, this same reasoning is not enough to prevent cheating elsewhere–Faith is not enough to explain the complete trust found in this system.
As it turns out, behavior within in subaks can be informed using game theory. The game has been played for centuries with families of the same farmers, so it is repetitive. Farmers live together and know each other, so cheating is always known. If one farmer is constantly cheating, others in the Subak can completely cut off the water supply, even exiling them from the community.
Since all farmers have incentives to cooperate, there is very little reason to cheat. However, in the larger scale community of all connected subaks, chemical fertilization has resulted in a significant problem.
Recently, there has been a push to have rice terrace farmers go back to organic farming. In order to be considered organic, the rice cannot be exposed to chemical fertilization. The problem arises because the farther the water is from the mountain, the more likely it is that a subak upstream has used chemical fertilizer, and that chemical fertilizer runs into all subaks downstream. Farmers farther down the stream are far less likely to cooperate in this game because they have imperfect information about the use of chemical fertilizer upstream.
In order to incentivise organic farming downstream, the farmers must all have access to information to see whether or not subaks upstream are using chemical fertilizers. In this sequential game, each subak must cooperate without any cheaters, or else farmers downstream have no reason to cooperate. This entire system is far more difficult to regulate and manage than the individual subaks. Hopefully it will be possible to build trust between all subaks so that organic farming will be possible both upstream and downstream.