Increased amounts of plain water have been recommended ad libitum during rehydration treatment with oral rehydration solutions (ORS) in moderately dehydrated cases in order to decrease the hypertonicity of ORS. However, we could not encounter any study demonstrating its effectiveness objectively. In this study, moderately dehydrated children admitted to Hacettepe University Ihsan Dogramaci Children's Hospital Diarrheal Disease Training and Treatment Unit were administered either standard WHO ORS treatment or two parts of standard WHO ORS and one part of plain water alternately at a dose of 100 ml/kg, according to the period they were admitted to the center. The frequency of vomiting, stool purging rate, and unscheduled intravenous treatment rate of the two different regimens were compared. There were 51 children in the standard ORS group and 79 children in the 2 : I ratio ORS group. The admission characteristics of the children were similar. The children with a stool purging rate over one per hour during treatment was higher in the standard ORS group (29.4 vs. 15.2 per cent, p = 0.051), as well as the children with vomiting (56 vs. 30 per cent, p = 0.007). The children who required unscheduled intravenous treatment was also higher in the standard ORS group (20 vs. 14 per cent, p = 0.2). A regimen of two parts of WHO ORS and one part of plain water may be an alternative treatment for moderately dehydrated children with non-cholera diarrhea in areas where hypotonic ORS is not yet available.