AIM: To compare the intraocular pressure (IOP) peaks and fluctuations using water drinking tests (WDTs) and mean diurnal IOP among Filipino patients with normal eyes and glaucoma suspects METHODS: This prospective study included normal and glaucoma suspect patients. Each patient underwent both WDT and mean diurnal examination on separate visits. For mean diurnal examination, IOP was recorded every 2h for 8h while in WDT, IOP was recorded prior to WDT, and post-WDT at 5, 15, 30, 45, and 60min. IOP peak was recorded as the highest IOP for both methods, and IOP fluctuation was recorded as highest IOP minus lowest IOP. RESULTS: With the comparison of diagnostic tests, both normal eyes and glaucoma suspect groups, the peak IOP was caught at 15min. Comparative analysis of both groups also showed that the peak IOP measurements were statistically higher for the WDT compared to mean diurnal IOP (P=0.039, P=0.048 under normal group and P=0.032 and P=0.031 under glaucoma suspect group). Similarly, the WDT had a statistically higher mean IOP fluctuation score than the mean diurnal IOP method in both groups (P=0.003, P=0.011 under normal group; P=0.002 and P=0.005 under glaucoma suspect group). CONCLUSION: This study shows that WDT is a comparable diagnostic exam in predicting IOP fluctuations than mean diurnal measurement. WDT is a promising diagnostic procedure for risk assessment in glaucoma.