The Peruvian plastic industry’s water tank manufacturing has increased by 22% since 2013. Regarding the annual sales data during 2014 – 2015, the industry in Peru ranks seventh in America behind the US, Mexico, Brazil, Argentina, Colombia and Chile. However, a portion of the companies in this category do not currently meet the estimated delivery time for final products, largely due to changes in configuration or format and unscheduled company stops, which generates losses in production. Thus, this study developed a methodology for optimizing production of domestic water tank manufacturers by applying lean manufacturing and preventive maintenance techniques that reduce lead time, delays and faulty equipment. The proposed model was validated in a water tank company where the implementation of the two proposals generated significant cost savings due to the elimination of waste in the processes of production. Our methodology reduced lead time by 2 days, eliminated unscheduled equipment stops and acheieved a percentage higher than 80% in the Overall Equipment Effectiveness (OEE), in addition to implementing good practices in process management.