Water.org's work on affordability is critical to increased access.
Water supply is a service that requires well-run utilities, fair tariffs, cost recovery, etc...too many forget this.
The sanitation sector, requires an even greater effort (due to the scale of the problem). Getting households onto the sanitation ladder is essential to improvements in health and reduction of disease and mortality. Interest rates, however, can be extremely challenging for the poorest of the poor.
Affordability is one piece of access. On WRI's blog, I argue that accountability is another.