The most common purity problem encountered in system employed to produce USP Purified Water is the control of microbiological contamination. While chemical purity is relatively easy achieve in a system which includes the proper components, microbiological contamination poses a much greater control challenge. The reasons for this include the fact that water purification system contain components which can support and encourage bacterial growth.

However by, employing sound engineering practised in the design of the purification system, exercising prudent management in the operation of the equipment and performing conscientious maintenance can assure the consistent and routine production of water containing microbiological contamination levels below the standards of the U. S. Pharmacopoeia.