Hand-powered reverse osmosis brings safe drinking water to off-grid rural India

Why safe drinking water remains out of reach

In many parts of rural India, the challenge of accessing safe drinking water is compounded by unreliable electricity, degraded aquifers, and the lack of cost-effective purification technologies capable of treating brackish or contaminated water. Despite decades of investment in piped supply systems and groundwater extraction, communities continue to depend on wells, reservoirs, and informal water sources that often fall outside regulatory oversight. The problem is especially acute in regions where climate change, salinisation, and groundwater depletion have altered local hydrological conditions. 

Against this backdrop, a field evaluation of a hand-powered point-of-use reverse osmosis system (HP-POU-RO) offers an important technological insight by demonstrating that high-quality drinking water can be produced without electricity, using only human force and an advanced ultra-low-pressure membrane. The study ‘Field evaluation of a hand-powered reverse osmosis system for sustainable water purification in off-grid rural India’, conducted over six months in Namkhana (West Bengal) and Udaipur (Rajasthan), focuses on the development, deployment, and performance of a new class of RO membrane reinforced with carboxymethylated cellulose nanofibers (CM-CNFs). 

These membranes were integrated into a compact, manually operated purification unit designed specifically for off-grid environments. The research by Kenji Takeuchi et al. highlights the potential of a portable, electricity-free RO system as a scalable drinking water solution for households living in resource-limited or disaster-vulnerable settings.

Water scarcity, salinity, and the limits of conventional purification

Rural India faces diverse and region-specific water challenges, shaped by both natural and anthropogenic factors. In the semi-arid region of Udaipur, the decline of surface and groundwater resources has made the city and its surrounding villages increasingly dependent on reservoirs and groundwater pumped from overexploited aquifers. Urban expansion, erratic rainfall, and the degradation of catchments have further reduced natural recharge. Hydrogeological assessments classify Udaipur's groundwater as overexploited, with extraction levels surpassing replenishable reserves.

Namkhana, by contrast, is a coastal region in West Bengal where households confront persistent salinization of shallow aquifers. Here, the intrusion of seawater, frequent cyclones, and tidal dynamics result in elevated concentrations of chloride, sodium, bicarbonate, and other ions in well water. While water is geographically abundant, safe drinking water remains scarce.

The innovation: An ultra-low-pressure RO system operated by human energy

The HP-POU-RO unit developed in this study integrates a 3-inch spiral-wound membrane module designed to function under extremely low hydraulic pressure conditions (≤0.2 MPa). This represents a significant deviation from typical household or community RO systems, which usually operate at 0.5 MPa or higher. The technical breakthrough is the adoption of a polyamide/carboxymethylated cellulose nanofiber (PA/CM-CNF) thin-film nanocomposite membrane, structured to improve hydrophilicity, permeability, and mechanical stability.

The membrane is produced through interfacial polymerisation on a porous polysulfone support, with CM-CNFs added to create a more open polymeric configuration and facilitate rapid water diffusion. This structural enhancement allows efficient brackish water desalination at pressures feasible through manual pumping, while maintaining strong salt rejection performance. Laboratory tests confirmed high water permeability (1.2–1.5 L/min at 0.5 MPa) and salt rejection exceeding 95%.

The mechanical system comprises a piston–cylinder pump connected to a 545 mm manual lever, operating on a rowing-motion principle. During each stroke, hydraulic pressure forces feedwater through the membrane, yielding permeate and rejecting concentrated brine. A 0.5-micron pre-filter removes suspended solids, and dual throttle valves regulate concentrate flow and internal pressure. For hygienic operation, at least 1.5 litres of water are discarded after periods of non-use, preventing diffusion-related contamination.

The resulting purifier is compact, portable, and does not require external electricity or combustion-based power, making it especially suitable for remote or disaster-prone areas.

Deployment in Namkhana and Udaipur

To evaluate the system under real-world conditions, researchers installed the HP-POU-RO units in selected households in Namkhana and Udaipur. Each site used different membrane variants:

• Namkhana: HA003 (ULP-RO membrane) + HA004 (commercial PA membrane for comparison)

• Udaipur: HA002 (ULP-RO membrane)

Users were trained to measure raw and purified water TDS, record temperatures, count strokes required per litre, and track daily water production. Water samples were also analyzed by an accredited laboratory using India’s drinking water standard (IS 10500:2012). Over six months, the system was subjected to local variations in water quality, temperature, user technique, and environmental conditions.

Before installation, RO modules were preconditioned, tested for membrane performance, and assessed for compliance with the Japanese water supply material leaching standard (JIS S 3200–7). These ensured that no harmful substances leached from system components and that the unit was safe for continuous potable water production.

Source water quality and purification outcomes

Source water conditions reflected the contrasting geographies:

• Namkhana well water had TDS levels between 685 and 692 mg/L.

• Udaipur reservoir water had TDS around 910 mg/L and exceeded acceptable limits for total hardness, alkalinity, calcium, and microbial contamination, including E. coli.

Other parameters—colour, turbidity, and taste—varied seasonally but often fell outside the desirable range for safe drinking water.

After purification through the HP-POU-RO system, both regions recorded TDS levels far below the 500 mg/L desirable limit:

• HA003 (Namkhana): 37 ppm

• HA002 (Udaipur): 78 ppm

• HA004 (commercial membrane, Namkhana): 54 ppm

All purified samples met the prescribed limits for turbidity, hardness, microbial contaminants, and chemical parameters. This demonstrated that even with minimal pressure, the ULP-RO membranes maintained strong and stable desalinization performance under field conditions.

Performance, stability, and energy efficiency

Hydraulic efficiency and water production

The manually powered systems produced meaningful volumes of purified water over the six-month period:

• HA002 (Udaipur): 28,050 litres

• HA003 (Namkhana): 5,475 litres

• HA004 (Namkhana): 2,343 litres

The HA003 module, in particular, demonstrated high recovery rates—around 70%, significantly higher than the HA004 commercial module (~40%). This translates into lower brine waste and higher water efficiency.

The number of strokes required per litre averaged:

• 54–55 strokes for HA002 and HA003

• 57 strokes for HA004

This small but consistent difference reflects the superior permeability and lower hydraulic resistance of the CM-CNF reinforced membranes.

Specific energy consumption 

One of the most striking results of the study is the extremely low energy requirement:

• HA002 & HA003: 0.18–0.20 kWh/m³

• HA004: 0.38–0.40 kWh/m³

For context, small-scale photovoltaic-powered RO units typically consume between 1.1 and 3.2 kWh/m³, even though they operate at much higher output volumes. The HP-POU-RO system therefore offers an order-of-magnitude improvement in energy intensity for low-volume household water purification.

Salt rejection stability

Over the entire testing period:

• HA003 maintained a TDS rejection of 93.94% ± 1.50

• HA004 maintained 95.25% ± 0.68

• HA002 maintained 88.20% ± 4.19

Variations were attributed to manual pumping inconsistency during initial usage, stabilizing as users became more familiar with the system.

User acceptance and usability

Although the system requires physical effort, the study found high user acceptance. Weekly feedback from participating households revealed strong satisfaction with taste, clarity, safety, and overall performance. Users scored the systems through a 5-point Likert scale, and the HA003 and HA002 units consistently rated high for:

• water quality

• cleanliness

• perceived health benefits

• overall satisfaction

The commercial HA004 membrane scored lower, mainly due to reduced ease of operation, lower recovery rates, and greater physical effort per litre.

The fact that users in both regions sustained regular operation for six months demonstrates the practical viability of the manual RO concept.

Limitations and future directions

Despite the system's overall success, the Hand Pumped Point-of-Use Reverse Osmosis (HP-POU-RO) system faces several limitations that primarily constrain its scalability and user-friendliness. The reliance on manual pumping fundamentally restricts the total daily water output, making the technology best suited for individual household-level use rather than larger community applications. This manual effort can also lead to user fatigue, particularly for vulnerable populations such as the elderly or physically challenged. 

Furthermore, the system's mechanical integrity requires attention; routine maintenance is necessary for components like seals and piston surfaces. Observations also point to initial pump stiffness, suggesting an immediate need for friction reduction and a better seal design to ensure smoother operation. Finally, achieving consistent system performance depends heavily on the user's technique, a variable factor that can compromise results, especially in the early stages of use.

To address these limitations and broaden the system's applicability, the study recommends a set of key improvements focused on enhancing efficiency, reducing user effort, and boosting water quality. Mechanical redesigns should prioritise refining the cylinder to increase displacement volume and thus reduce the number of strokes required per litre, while also optimising the lever geometry to minimise the physical effort required from the user. For regions with higher water demand, the integration of hybrid manual-solar systems is recommended to achieve a greater overall output. On the water treatment front, the focus should be on enhancing membrane resistance to common issues like biofouling and chemical degradation. Additionally, integrating an activated carbon post-treatment module is suggested as a solution to improve the water's taste and odour. These strategic improvements are necessary to strengthen the HP-POU-RO system's role in supplying clean water to populations facing higher demand or having unique physical vulnerabilities.

A practical, sustainable model for off-grid water purification

The hand-powered point-of-use RO system presented in this research offers an important contribution to decentralised water purification technologies. By combining a manually operated hydraulic pump with a high-performance ultra-low-pressure membrane, the device demonstrates that safe drinking water can be reliably produced without electricity, complex infrastructure, or expensive maintenance.

In regions like Namkhana and Udaipur—representing two different forms of water stress—the system consistently converted brackish, microbially contaminated, and chemically imbalanced water into potable water meeting national standards. With specific energy consumption as low as 0.18–0.20 kWh/m³, the system provides an exceptionally energy-efficient alternative to solar or electrically powered RO units.

For households living in off-grid or disaster-prone areas, this technology offers a resilient, low-cost, and environmentally sustainable option for safe drinking water. While improvements are needed to enhance user comfort, scale up production, and expand capacity, the study demonstrates a viable model for addressing water scarcity in rural India through innovation grounded in simplicity, energy independence, and community acceptance.

This study shows that safe drinking water can be produced without electricity, using a simple hand-powered system and advanced low-pressure membranes. For off-grid households, disaster-prone regions, and areas with saline or contaminated water, such systems offer a practical alternative to electric or solar RO units. While not a replacement for public water systems, they can fill critical gaps where infrastructure is weak or unreliable. With further refinement, hand-powered reverse osmosis could become a useful tool in India’s wider effort to ensure safe drinking water for all.