Produced water treatment systems remove oil from produced water during development well testing and clean-up. Produced water require further treatment before it can be safely discharged. By using the compact vessels containing oil adsorption filter cartridges water can be efficiently treated . These can be configured to handle a range of process contaminants. The vessels are mounted in a self-contained compact skid. Each skid has two vessels for either parallel or series operation, depending on the required clean-up duty.