Abstract: Data warehouse forms an integrated environment where data from disparate systems is bought together and presented in a consistent matter. Based on the data present in the warehouse business users want to make key decisions. In order to support these decisions, quality of data in warehouse must be reliable. If there are issues in data loaded in warehouse, business users lose trust and the information from the warehouse becomes unreliable. One of the essential components of data warehouse is the (Extract, Transform and Load) ETL process. This process is used in most organizations to load data into the warehouse. An ETL is a complex process in itself and one which is most time consuming during the building of the data warehouse. It allows the data in the warehouse to be refreshed on the periodic basis (daily, ‘maintained and there is no data loss every time data is loaded into the warehouse using ETL.