There is growing evidence that dams do not fulfill the economic promises made for them: they cost more than claimed, they fill with silt long before promised, and they produce less power than expected. Dams also assist the powerful and wealthy to enclose the common land, water and forests of the politically weak.

For a variety of reasons, dams are becoming more expensive. These reasons include:

• increasing technical and construction problems encountered in building dams (e.g. dealing with sedimentation--lower lifespan of dams).
  
• increasing requirements to pay for mitigation of social and environmental impacts.
  
• delays due to public opposition and other problems.
  
• the fact that most of the best sites have already been taken.

Hydropower is also a highly inflexible source of power, vulnerable if demand for power changes from that projected. A large hydro project typically takes a decade from the start of construction to providing power. During that time, power demand may change greatly, sometimes eliminating demand for the power to be produced by that dam. For
example, the Bakun Dam is now justified on the basis of rapidly increasing power demand (13%/year). However, if there is a severe recession between now and 2003, and this growth in demand slows down, or stops, then Malaysia could be left with an expensive dam, and no demand for its product. This has happened in other countries, including Argentina and Columbia. Such problems have contributed to indebtedness of numerous countries that have invested large sums in large dams.

Increasing economic inequalities: In many instances, dams, and related facilities, like irrigation projects, have benefited disproportionately those members of society that are already wealthier. This is because, as in the case of irrigation projects, larger landowners, whether individuals or corporations, are better able to afford the additional machinery,
chemicals, and labour that will be needed to benefit from the extra water. Small farmers, on the other hand, risk losing their share entirely of the water, or of being bought out or forced off their land by landowners who are in position to use the land.