Unintended consequences can be roughly grouped into three types:
- A positive, unexpected benefit (usually referred to as serendipity or a windfall).
- A negative, unexpected detriment occurring in addition to the desired effect of the policy (e.g., while irrigation schemes provide people with water for agriculture, they can increase waterborne diseases that have devastating health effects, such as schistosomiasis).
- A perverse effect contrary to what was originally intended (when an intended solution makes a problem worse), such as when a policy has a perverse incentive that causes actions opposite to what was intende