Type 2 diabetes mellitus is a chronic disease characterized by hyperglycemia and may be accompanied by psychological problems, including anxiety. Oral water therapy is a simple complementary intervention that may support blood glucose control; however, its effects on blood glucose levels and anxiety require further investigation. This study aimed to determine the effectiveness of oral water therapy in reducing blood glucose levels and anxiety among patients with type 2 diabetes mellitus at Sriwijaya General Hospital, Palembang. This quantitative study employed a quasi-experimental pretest-posttest design. A total of 42 respondents were divided into a blood glucose group and an anxiety group, with 21 respondents in each group. The intervention consisted of consuming eight 200-mL glasses of water daily for seven days. Blood glucose levels were measured using a glucometer, while anxiety was assessed using the Hamilton Anxiety Rating Scale (HARS). Data were analyzed using the paired-samples t-test and Cohen's d. Blood glucose levels decreased across all measurement days, from 232.7 to 218.2 mg/dL on day 1, from 218.9 to 204.8 mg/dL on day 3, from 203.5 to 191.5 mg/dL on day 5, and from 189.8 to 177.4 mg/dL on day 7. All changes were statistically significant (p < 0.001), with very large effect sizes (Cohen's d = 2.907–3.739). In contrast, anxiety scores did not show a statistically significant change (p > 0.05), with very small to small effect sizes. Oral water therapy may support blood glucose control as a complementary intervention but did not demonstrate a significant effect on anxiety.