International Field Testing of a Portable Optical Interaction Assay in Municipal Tap Water: Singapore and the Philippines (April 2026)

Abstract To evaluate geographic generalizability beyond the United States, the EcoExposure™ portable zero-shear optical interaction assay was field-tested in two independent Southeast Asian municipal tap-water systems: Metro Manila / Quezon City (Philippines) on April 11, 2026, and Singapore on April 12, 2026. Despite marked differences in source water, treatment infrastructure, mineral/ionic profiles, and distribution systems, both locations produced consistent, interpretable reaction patterns—including progressive central clearing, structured aggregate organization, and reproducible time-dependent kinetics. These results, obtained under real-world lighting conditions and with both correct and under-dosed reagent levels, demonstrate that the core Z-site interaction mechanism is robust across diverse international municipal drinking-water matrices and support broader global deployability of the platform.

1. Manila / Quezon City Tap Water (Philippines), April 11, 2026 Quezon City tap water, supplied by Manila Water Company (East Zone), draws primarily from the Angat Dam reservoir system with supplemental treatment from Laguna Lake. Samples were collected directly from the same household sink and analyzed immediately using the standard zero-shear workflow (dry reagent addition, no mixing, top-down imaging at 15 and 30 minutes).

Dose Effects

• Correct-dose samples showed strong aggregate formation and complete optical development.

• Under-dosed samples retained the same kinetic progression and central clearing, but with lighter, more subtle signals—consistent with incomplete Z-site occupancy.

These findings confirm that suboptimal dosing reduces signal intensity rather than abolishing the reaction, while the underlying interaction mechanism remains intact.

Lighting Robustness Images captured under irregular room lighting (non-uniform indoor illumination) remained interpretable in the central analysis region. Kinetic progression and structured organization were clearly visible, demonstrating that perfect photobox lighting is preferred but not required for field use.

2. Singapore Tap Water, April 12, 2026 Singapore tap water is produced by the Public Utilities Board (PUB) under the “Four National Taps” strategy (local catchments, imported water, NEWater recycled water, and desalinated seawater). It consistently meets or exceeds WHO Guidelines for Drinking-water Quality and Singapore’s strict national standards.

Two independent samples were tested using the identical zero-shear workflow. Unexpectedly, Singapore samples exhibited the exact same general optical behavior observed in prior U.S. and Manila experiments: progressive central clearing, structured aggregate organization, and highly reproducible kinetics across timepoints and samples.

Notable Context PUB has conducted biennial microplastic surveillance since 2017. Testing in 2015, 2017, and 2021 detected no microplastics in treated drinking water (raw-water sources showed only low levels, <10 particles per litre). No public nanoplastics data specific to Singapore tap water exist, but the consistent absence of detectable microplastics in finished water makes Singapore an especially rigorous test case for assay sensitivity.

3. Overall Interpretation and Conclusion Across three distinct municipal systems—prior U.S. tap water, Metro Manila/Quezon City, and Singapore—the portable optical interaction assay demonstrated consistent, interpretable reaction patterns. The core Z-density-driven mechanism is preserved despite substantial differences in raw-water sources, treatment processes, ionic/mineral composition, and distribution infrastructure.

Key Findings

• Successful performance in two independent Southeast Asian municipal systems

• Robust signals under both correct and under-dosed reagent conditions

• Interpretable results under real-world (non-ideal) lighting

• Core interaction behavior preserved across geographically and chemically diverse finished drinking-water matrices

• Strong support for international and global decentralized deployment potential

These international field results strengthen the generalizability claimed in the Z-Model provisional (63/929,618) and optical classification provisional (64/017,359). The platform is well-suited for scalable, decentralized environmental monitoring in diverse municipal settings worldwide.

Keywords: microplastics, nanoplastics, portable optical assay, international validation, municipal tap water, decentralized monitoring, EcoExposure, Z-site interaction, zero-shear assay This paper is also available at: https://doi.org/10.5281/zenodo.19673596