The modular water treatment system produces potable water using no moving parts, no energy and no harmful chemicals. The unit utilizes slow sand filtration to produce potable water for use in rural or remote locations, developing areas and locations with limited power. A proprietary pre-filter improves the performance of the slow sand filtration system. The system removes up to 99.99-percent of bacteria, viruses, Giardia and Cryptosporidium. The World Health Organization has called slow sand filtration the cheapest, simplest and most efficient method of water treatment, according to the manufacturer. Slow sand filtration is approved world-wide for treatment of surface water by USEPA, WHO, OXFAM and others. The singular modular unit incorporates settlement, straining, filtration, organism removal, organism inactivation, chemical change and some storage capacity. It prepares water for subsequent chlorination with maximum efficiency. The system includes a proprietary epoxy coated modular tank, which provides low up front capital costs and lasts 3-4 times longer than a typical painted steel tank. No pumps or motors are required, as the system uses a gravity flow process. The modular design allows for simple and fast on-site construction.