Abstrak: Penelitian ini bertujuan untuk mengkaji pengaruh diameter dan ketebalan pasir silika pada saringan pasir lambat (SPL) dalam menurunkan parameter kualitas air seperti kekeruhan, Total Padatan Terlarut (TDS), pH, Chemical Oxygen Demand (COD), dan Total Coliform pada air Sungai Remeneng, Kecamatan Narmada, Kabupaten Lombok Barat. Air sungai yang digunakan sebagai sumber utama kebutuhan sehari-hari penduduk telah tercemar oleh limbah domestik dan pertanian yang menyebabkan kualitas air menurun. Penelitian dilakukan dengan variasi ketebalan pasir (10 cm, 15 cm, 20 cm, dan 25 cm) dan variasi diameter pasir silika (10 Mesh, 20 Mesh, dan 30 Mesh). Hasil penelitian menunjukkan bahwa SPL mampu menurunkan nilai kekeruhan, TDS, pH, COD, dan Total Coliform secara signifikan. Nilai kekeruhan terbaik diperoleh dari ketebalan 25 cm dan diameter 30 Mesh sebesar 19,8 NTU. Sedangkan penurunan COD dari 104 mg/L menjadi 90 mg/L dicapai pada ketebalan 25 cm dan diameter 10 Mesh, meskipun nilai COD tersebut masih melebihi baku mutu 80 mg/L sesuai dengan Peraturan Pemerintah No. 22 Tahun 2021. Parameter Total Coliform juga mengalami penurunan yang cukup signifikan, dengan hasil terbaik pada ketebalan 25 cm dan diameter 10 Mesh sebesar 230 mpn/ml. Kesimpulannya, saringan pasir lambat dengan variasi ketebalan dan diameter pasir silika efektif untuk menurunkan parameter kekeruhan, TDS, pH, dan Total Coliform, namun untuk parameter COD, meskipun terjadi penurunan, namun hasilnya masih belum memenuhi baku mutu.Abstract: This study aims to assess the effect of diameter and thickness of silica sand on slow sand filters (SPL) in reducing water quality parameters, such as turbidity, Total Dissolved Solids (TDS), pH, Chemical Oxygen Demand (COD), and Total Coliform, in Remeneng River water, Narmada District, West Lombok Regency. River water used as the main source of daily needs of the population is polluted by domestic and agricultural waste, which causes water quality to decline. The research was conducted with sand thickness variation (10 cm, 15 cm, 20 cm, and 25 cm) and silica sand diameter variation (10 Mesh, 20 Mesh, and 30 Mesh). The results showed that SPL was able to significantly reduce turbidity, TDS, pH, COD, and Total Coliform values. The best turbidity value was obtained from a thickness of 25 cm and a diameter of 30 Mesh of 19.8 NTU. While the decrease in COD from 104 mg/L to 90 mg/L was achieved at a thickness of 25 cm and a diameter of 10 Mesh, although the COD value still exceeds the quality standard of 80 mg/L in accordance with Government Regulation No. 22 of 2021. The Total Coliform parameter also experienced a significant decrease, with the best results at a thickness of 25 cm and a diameter of 10 Mesh of 230 mpn/ml. In conclusion, slow sand filters with variations in thickness and diameter of silica sand are effective for reducing turbidity, TDS, pH, and Total Coliform parameters, but for COD parameters, although there is a decrease, the results still do not meet the quality standards.