This has been proven in countries where access to soap is limited. In rural Bangladesh, where diarrhea among children is a widespread problem, scientists examined the effectiveness of four different forms of hygiene on incidences of diarrhea. Some study participants were observed preparing their family's meals without washing their hands after using the bathroom. Others were observed washing one hand using water only; still others were seen washing both hands with water; and lastly, scientists saw some food preparers wash at least one hand with water and soap. While taking detailed notes on the manner and opportunities for handwashing, researchers also conducted monthly diarrhea tests on the children in each household in the study.

Here's what they found:

In households where food was prepared without washing hands, children had diarrhea in 12.5% of monthly assessments compared with 8.3% in households where one hand was washed with water only, 6.9% where both hands were washed with water only, and 3.7% where at least one hand was washed with soap. Food preparers commonly washed one or both hands with water only, but fieldworkers observed food preparers washing at least one hand with soap in only three households (1%).

Through the use of water alone on both hands, the rate of diarrhea was cut by nearly half. Not bad for a little H2O. Adding in soap had a predictable effect, cutting the prevalence of diarrhea again by another 3.2 points, but the gains from soap clearly weren't as high as from scrubbing with water. So, while avoiding soap if it's available is still a missed opportunity to remove germs, rinsing isn't so pointless, either. Maybe we should withhold our judgment.

Is soap always clean? This may be disappointing to diehard germaphobes, but it's possible for soap to be crawling with bacteria as much as anything else. If you're storing your soap improperly, such as leaving it in a wet puddle on the edge of your sink, it gives bacteria a fertile place to multiply. When you use it, you basically wind up transferring germs from the soap directly to your hands.

In a thorough study of soap contamination, one team of U.S. researchers found that even among test subjects with great handwashing technique -- more on that in a minute -- soap that was already contaminated wound up increasing the number of bacteria on the subjects' hands after washing. The scientists tested three types of soap dispenser, in both lab and real-world settings. Of the three variants, the dispensers that were refillable from a giant bottle of liquid soap were by far the filthiest, leading to a 26-fold increase in handwashers' bacteria levels. Modular dispensers that relied on sealed refills stayed clean even after a year of use. In short, both the nature of the dispenser as well as the cleanliness of the soap itself can have a major impact on how clean your hands are after washing.