Pengaruh Waktu Kontak terhadap Efisiensi Penyisihan Zat Organik (KMnO4), Kekeruhan, TDS, pH, dan Escherichia coli pada Pengolahan Air Hujan dengan Kombinasi Media Filter Polypropylene dan Lampu Ultraviolet = The Effect of Retention Time on the Removal Efficiency of Organic Substances (KMnO4), Turbidity, TDS, pH, and Escherichia coli in Rainwater Treatment with Combination of Polypropylene Filter and Ultraviolet Light