<p>Nanofiltration is an effective technology for producing clean water through the removal of harmful pathogens, micropollutants and ions. However, its dependence on a power supply and complex configuration hinder the deployment of nanofiltration systems in underserved regions. To support universal access to clean water in these regions, we have developed an ultrapermeable polyamide nanofiltration membrane that can be used in an electricity-free portable purifier. The membrane features a nature-inspired substrate that mimics the highly efficient fractal transport structures found in leaves and blood vessels. The polyamide nanofilm supported by this unique fractal substrate achieved a record-high permeance of 113.6 l m⁻² h⁻¹ bar⁻¹, an order of magnitude higher than current commercial benchmarks. The design enabled rapid water purification by simple manual vacuum pumping, producing over 250 ml of pure water within 15 min using small palm-sized membrane disks with an area of 157 cm². Furthermore, the nanofiltration membrane exhibited 98.0% Na₂SO₄ rejection, along with exceptional removal of pathogens (&gt;99.9999%) and micropollutants (for example, 99.1% of perfluorooctanesulfonate). By delivering high-quality purified water without the need for any electricity, this portable purifier offers a practical solution that is aligned with the United Nations Sustainable Development Goal 6, focusing on clean water and sanitation.</p>