RO Flushing Procedure (Manual)

May 29, 2021


A straightforward procedure for the removal of foulants is to flush the system with flushing water. Flushing scours the membrane surface by taking advantage of high velocity at low pressure. A large volume of flush water is required. This procedure can be an effective method for removing light organic fouling provided it is applied before there is a significant performance decline. 

General operating conditions for flushing are as follows:

Flushing water Use pre-treated feed water (refer toTable 1) or RO product water. Flushing water should not contain any oxidants. Maintain flushing water pH range between 3.0–8.5.
Table 1: Flushing water of various RO feed water treatment systems
RO feed water type Flushing water
Sea water Pre-treated feed water
Brackish water Pre-treated feed water
Waste water RO product water
High pH feed water (i.e., 2nd pass high pH feed water) Pre-treated feed water without NaOH 1st pass product water without NaOH
Pressure Low pressure (0.1–0.2 MPa [15–30 psi])
Water flow rate High flush water flow rate is best but do not exceed the recommended vessel pressure drop. Limit pressure drop to max 0.2 MPa [30 psi] per stage.
Maximum feed flow rate per vessel 8-inch element: 200 L/min (53 gpm) 4-inch element: 50 L/min (13 gpm)
Temperature ≤ 40°C (104°F)
Period 0.5–1.0 hour

It is important to keep the permeate side isolation valve(s) open to keep the permeate back pressure to a minimum during the flushing procedure. 
Feed/brine pressure should always be higher than permeate pressure to avoid any membrane damage. 

INSTRUCTION. Flush each stage (bank) separately. Do not re-circulate flushing water.

The data and information contained in this document are based upon rigorous technical testing by Toray, and is to the best of our knowledge reliable. Toray cannot control design and operating conditions, and consequently Toray does not assume any liability for results obtained or damage incurred through the application of the information provided herein. No liability, warranty or guarantee of final product performance by Toray is implied by the information provided in this document.
This manual supersedes all previous versions. Technical modification of products or production technology may necessitate changes to information in this manual without prior notice. Please verify that your version of the manual is the latest version available by either contacting Toray, or checking online at

This content is extracted from Toray’s “Toray RO Handling Manual (Version. Apr. 2021)” (the Manual). Please refer to other contents stated in the Manual. When using this content, please read the Terms and Conditions of Use stated in the manual and agree to them before using this content.