Customer Login
+44 (0)1604 660 811

The control of the chemical purity of water, used for the disinfection and sterilisation of medical devices, is critical to ensure effective decontamination and the longevity of both the machines and equipment used for automated processes. High levels of solids and minerals in the water supply can lead to interference with detergents and disinfectants and deposits building up within the machine creating favourable conditions for bacterial growth and biofilm proliferation.

Existing standards and guidelines including; ISO 15883-1, ISO 15883-4, EN 285, CFPP 01-06, CFPP 01-01 and the superseded HTM2030 and HTM2031, all detail the required testing and acceptable limits required for water, that is used for the decontamination of medical devices. Particular importance is placed on final rinse water quality to prevent recontamination of clean devices.

The majority of Endoscopy departments use the process of Reverse Osmosis (RO) to remove impurities from water prior to use in washer disinfectors. RO treatment plants remove almost all dissolved inorganic contaminants by passing the water, under pressure, through a semi-permeable membrane against an osmotic gradient. As well as having the capability to remove particles as small as ions such as those of sodium and magnesium, the process also removes a high proportion of organic material, bacterial endotoxins and microorganisms. Some RO units are fitted with a final 0.2µm filter to control bacterial numbers.

The quality of the water used for the disinfection and final rinse of medical devices is required to be analysed on a regular basis. Electrical conductivity, hardness and pH are tested on weekly water samples and full chemical purity screening is conducted on a quarterly and/or annual basis depending on which standard or guidelines are being followed.

Specified Limits

Properties HTM2030 CFPP 01-06 HTM 2031 CFPP 01-01 (Part D) EN 285 / CFPP 01-01 (Part C)
Appearance Clean, colourless and free of particulate matter Clear, bright & colourless Clear, colourless Clear, colourless Colourless, clean without sediment
Electrical Conductivity RO Water  <30 µS cm-1 <40 µS cm-1 ≤35  µS cm-1 ≤30  µS cm-1 Corrosion: ≤3  µS cm-1,  Load: ≤30  µS cm-1
Electrical Conductivity Potable Water <300 µS cm-1 <200 µS cm-1
Total Dissolved Solids (TDS) <4 mg/ 100 ml <4 mg/ 100 ml
Total Organic Carbon (TOC) < 1 mg/l
Hardness (as CaCO3) <210 mg/l <50 mg/l
Hardness (final rinse or steam) <50 mg/l ≤0.02 mmol/l
pH 5.5 – 8.0 5.5 – 8.0 5.5 – 8.0 5 – 7
Chloride <120 mg/l ≤ 0.5 mg/l <10 mg/l Corrosion: ≤ 0.1 mg/l,  Load: ≤ 0.5 mg/l
Chloride in final rinse/steam <10 mg/l
Iron <2 mg/l <2 mg/l
Cadmium  –  –  –  – ≤ 0.005 mg/l
Silicate <0.2 mg/l ≤ 0.1 mg/l <0.2 mg/l ≤ 0.1 mg/l
Phosphate(P2O5) <0.2 mg/l ≤ 0.1 mg/l <0.2 mg/l ≤ 0.1 mg/l
Heavy Metals (as lead) <10 mg/l ≤0.1 mg/l <10 mg/l ≤ 0.05 mg/l
Heavy Metals other than Fe, Cd, Pb  –  –  –  – ≤ 0.1 mg/l
Acidity/Alkalinity Not Quantified
Ammonium (NH4) ≤ 0.2 mg/l ≤ 0.2 mg/l
Oxidisable Substrates Not Quantified Ra (Load)
Nitrate (N03) ≤ 0.2 mg/l ≤ 0.2 mg/l
Sulphate Not Quantified Ra (Load)
Residue on Evaporation ≤ 30 mg/l ≤ 30 mg/l
Calcium and Magnesium Not Quantified Ra (Load)


To avoid the risk of corrosion, water used in the cleaning of stainless steel instruments should have a chloride concentration less than 120 mg/L and, for final rinse/disinfection, less than 10 mg/L Cl–. Chloride concentrations greater than 240 mg/L Cl– cause pitting to occur.

Heavy Metals

Heavy metals are generally toxic in low concentrations and, as far as possible, should be absent from water used to process items that will be used invasively.  Tarnishing of stainless steel instruments, shown by blue, brown or iridescent surface coloration, occurs when heavy metal ions, such as iron, are present in the process water. In hot water (over 75°C) magnesium ions and silicates can cause similar discoloration.

Total Dissolved Solids

Total Dissolved Solids (TDS) cannot be removed with mechanical filtration or standard carbon filtration. A Reverse Osmosis system is one of the most effective means of filtering total dissolved solids from a water supply. With an RO system the TDS level increases on the high pressure side of the membrane as water permeates through the membrane to the low pressure side. The water containing the high level of TDS is flushed down the drain leaving the water with minimal total dissolved solids available for immediate use.


The pH of pure water is pH 7.  Changes in the pH can be contributed to by the type of bedrock and environmental conditions the water has flowed through.  The removal of chemical and mineral impurities from water through a process such as reverse osmosis can alter the pH of the water prior to use.  Water that is not within the permissible range according to the guidelines can have an impact on the efficacy of the detergent and disinfection cycles of the decontamination process.


As with pH, the level of hardness depends upon the type of conditions that the water flows through, for example; water that has flowed through areas rich in peat is low in the minerals that contribute to hardness, whereas the chalk bedrock of East Anglia creates very hard water which in turn creates unwanted limescale deposits within the water delivery systems.  Limescale can also provide a rough textured surface in which microorganisms are protected from manual cleaning and disinfection.  In addition, high levels of hardness can interfere with disinfection efficacy.  European Norms therefore require that ‘hard water’, as a superior challenge, is used in testing the efficacy of a chemical disinfectant.

Out of specification

Out of specification results observed when measuring the chemical purity of the water, generated by Reverse Osmosis Systems and used in Endoscope Washer Disinfectors, are usually an indication of a problem with the RO system.  Problems can be caused by fouled, broken or exhausted membranes.  In such instances it is recommended that the RO supplier is contacted to inspect the membranes and the RO system.  In cases where the membranes are found to be clean and undamaged or where remedial action to the RO system does not resolve the problem, it is recommended to check the chemical purity of the incoming water prior to the RO system to check that there is not an issue with the incoming water source.

20/30 Labs asked an independent medical device validation company to assess the maximum air pressure that the ISO 15883 Dry Cabinet Surrogate Devices could withstand.  Forcing air through the device would not give a pressure higher than atmospheric pressure, as the air simply passed through the device.  To obtain a pressure greater than atmospheric pressure, individual sections of the surrogate device were isolated by clamping and air forced through.  Each section of the device was tested by this method and was able to withstand the maximum pressure that the testing equipment could produce: 3.8 bar.

Hospital Analysis

A vast suite of standard and specialist analyses are available. Read More

Potable Water Testing

A range of tests available as required by the MODW and HTM 04-01. Read More

Pseudomonas Aeruginosa

The detection and enumeration of Pseudomonas aeruginosa according to HTM 04-01 and the MODW. Read More

Legionella Testing

Accredited to ISO 11731-2:2008 to carry out detection and enumeration of Legionella. Read More

Get in Touch

If you would like to speak to someone regarding sample analysis, testing scope or advice, please do not hesitate to contact us:

Upcoming Events

  1. Basic Microbiology Study Day

    November 22 @ 11:00 am - 3:00 pm
  2. Basic Microbiology Study Day

    December 13 @ 11:00 am - 3:00 pm