Water re-use and recycling projects can be one of the most difficult water treatment processes to design and implement. They often require a combination of chemical and mechanical solutions. They must also be designed by someone familiar with water quality requirements, air and water permitting, and the nature of plant operational cycles. While it is easiest to design a greenfield plant to operate with a water re-use, or ZLD system, any plant in operation today must look to retrofit existing equipment. Generally speaking, the simplest and lowest cost option is to install equipment at the front end (raw water intake) to minimize waste water generation at the back end of the plant (i.e. cooling tower blowdown). 

Because there is no single design that works for all applications, it is important to find the right, integrated solution for each plant. In order to create a successful water treatment system design for a plant, it is necessary to have a thorough understanding of the chemistry and equipment aspects and plant conditions: plant design, operating conditions, available water quality and quantity, available personnel and training, capital and operating budgets, and environmental restrictions. Most water re-use and ZLD systems use one or multiple of the following water treatment technologies, in order of capital costs: chemical feed systems, membrane filtration, reverse osmosis, evaporation ponds (if climate allowable), cold lime softening and evaporation/crystallization. While evaporation/crystallization may seem like the simplest solution, its initial capital investment and ongoing energy costs greatly exceed all other technologies combined.