New standards in medical water treatment:

Legal certainty medical water treatment with new water limit values

Do you use water in accordance with the DIN EN 285 standard in your reprocessing unit for medical devices (AEMP)? Attention: These standard values may no longer correspond to the current state of knowledge, which could jeopardize the legal safety of your reprocessing processes. The potential risks and recommended measures are explained in detail in this article.

Efficient and legally compliant reprocessing for cost efficiency

Although DIN EN 285 is currently still the standard for water quality in medical device reprocessing, it no longer reflects the latest state of knowledge. Since 2022, technical guidelines have advised stricter limit values, which could soon be legally binding. In order to be legally compliant, many hospital management teams and those responsible for AEMP are already adapting their processes to these new requirements, which not only provides legal certainty but also leads to immediate cost savings.

DIN EN 285: Need to expand to include modern new limit values

The relevance of DIN EN 285 for large steam sterilizers is in question. It no longer meets the requirements of modern sterilizers, which require high water and steam quality. Facilities that rely exclusively on DIN EN 285 are exposing their instruments and medical devices to potential damage. The Instrument Reprocessing Working Group (AKI) recommended stricter guideline values back in 2017, which were adopted by the DGSV's Hygiene, Construction and Technology Committee in its recommendation no. 17 from April 2022 in order to update the standards for water quality.


DIN EN 285, Table B 1 for pure steam generators

DGSV Technical Committee 2022

Conductivity at 25 °C

≤ 5 µS/cm

≤ 0.1 µS/cm


≤ 1 mg/l

≤ 0.4 mg/l

The conductivity serves as an indicator of the ion concentration in the water. A higher conductivity indicates a greater distance from the ideal of fully demineralized water. Sodium, calcium, magnesium and chlorine ions, which influence conductivity, can damage medical instruments. However, silicates, which are salts containing silicic acid and cause deposits on instruments, are not detected by conductivity measurements. It is therefore necessary to monitor silicate levels as well, as high silicate concentrations can damage water treatment systems. Many facilities neglect this important control.

Instrument damage in concrete terms

How do your instruments specifically suffer from unwanted substances in the supposed deionized water? The three most important types of damage:

  • Scale deposits
  • Pitting corrosion
  • Silicate deposits

Limescale deposits

Limescale stains and deposits caused by calcium and magnesium salts are not a hygiene concern, but require additional work for the AEMP team to remove manually. Monitoring water hardness helps to prevent these deposits from forming.

Pitting corrosion

Pitting corrosion caused by chlorides and other halogen salts poses a serious hygiene risk, as larger, germ-infested holes can form under small areas of corrosion.

Silicate deposits

Silicate deposits, which appear as brownish or bluish discolorations, impair visual inspection and can lead to corrosion in the long term. They are difficult to remove and can impair the traceability of instruments

Scale deposits put a strain on the budget

Calcification, corrosion and silicate deposits are visible signs of poor process water quality in medical instruments, washer-disinfectors and sterilizers. A study by HeylNeomeris from 2019 shows the financial impact: One clinic used 87.55% of its annual budget on repairs and replacement purchases in just six months, which meant a potential annual budget overrun of 75.11%, or €87,500 in additional costs. This also has a negative impact on the clinics' sustainability goals, as frequent new purchases waste resources. Insufficient deionized water quality therefore causes considerable costs and damage to sustainability.

Also a building block for patient safety!

Patient safety as a priority: Hygienic risks, such as germ contamination and impurities, threaten successful sterilization and therefore patient safety. Medical facilities must put patient safety above economic considerations. Nosocomial infections, caused in part by inadequately reprocessed instruments, lead to numerous deaths every year. According to the MPBetreibV, the responsibility for reprocessing lies with the operators. Non-compliance can have legal consequences. State-of-the-art water reprocessing ensures legal certainty and patient safety and goes beyond the requirements of DIN EN 285.

How water treatment works

A demineralized water production system for sterile processing combines several components. The DGSV expert committee explains the individual treatment stages in recommendation no. 17. These include filters, ion exchangers, reverse osmosis systems, membrane degassing, electro-deionization systems (EDI), mixed-bed exchangers and a tank for the finished deionized water. Monitor water parameters at various points in the process to ensure measured values meet the correct limits. Redundant system design and an emergency bypass system keep operations running smoothly even in the event of a failure.

With HeylNeomeris for optimum water quality

In order to bring an existing water treatment system up to date, a comprehensive analysis is first required. This requires consideration of many factors, from the water source to the operating personnel. An independent expert company can carry out this analysis to identify weak points and suggest improvements. The aim is to make optimum use of existing systems and, if necessary, incorporate new technologies or specialist companies. Such adaptations can be carried out in both large hospitals and smaller clinics, as a reference project in Hanover shows.

Legal certainty in reprocessing? Only with up-to-date water treatment!

In summary, it can be said that the limit values in DIN EN 285 for water treatment during steam sterilization are no longer up to date. They can lead to instrument damage and high operating costs, which impairs the safety of processes and therefore legal certainty in medical facilities. The DGSV expert committee sets new, up-to-date limit values. Find out about the necessary adjustments in your facility, as legally compliant reprocessing requires compliance with current standards.