HM Digital AP-1 AquaPro Water Quality Tester (TDS) and Temperature Quality Product ~ Designed in USA HOW PURE IS YOUR WATER? Know when to change your water filter Measure and Monitor Total Dissolved Solids (TDS) levels for Drinking Water Water Filters Hydropoinics Aquariums Food &Coffee Pools & Spas Colloidal Solver The United States EPA's Maximum Contaminant Level for Total Dissolver Solids (TDS) for human consumption is 500ppm. HM Digital introduces its new Aqua Pro series, a line of handheld TDS/EC meters with a sleek design that's perfect for today's modern kitchen. The Aqua Pro digital water testers are the next generation for today's tech-savvy and health-conscience consumer.