We conducted a study in a squatter settlement in Karachi, Pakistan where residents report commonly washing their hands to determine if providing soap, encouraging hand washing, and improving wash-water quality would improve hand cleanliness. We allocated interventions to 75 mothers and collected hand-rinse samples on unannounced visits. In the final model compared with mothers who received no hand-washing intervention, mothers who received soap would be expected to have 65% fewer thermotolerant coliform bacteria on their hands (95% CI 40%, 79%) and mothers who received soap, a safe water storage vessel, hypochlorite for water treatment, and instructions to wash their hands with soap and chlorinated water would be expected to have 74% fewer (95% CI 57%, 84%). The difference between those who received soap alone, and those who received soap plus the safe water vessel was not significant (P = 0·26). Providing soap and promoting hand washing measurably improved mothers' hand cleanliness even when used with contaminated water.