Hemodialysis Water System

The hemodialysis water system is a system that reduces the amounts of various substances and contaminants known to be toxic to the dialysis patients in the water. With these systems, water needs for various purposes such as dialysate preparation, concentrated dialysate preparation and preparation of the dialyzer for re-use are met at appropriate flow, pressure and temperature.

According to Turkey Ministry of Health and the European Pharmacopeia, maximum contamination level of pure water for hemodialysis and the maximum bacteriological levels are shown in Table 1 and Table 2 respectively.

Table 1: Maximum Contaminant Levels

Parameter

Maximum level

Parameter

Maximum level

Acidity - Alkalinity

Test conformity

Calcium

2 ppm

Oxidizing substance

Test conformity

Magnesium

2 ppm

Total Chlorine

0.1 ppm

Mercury

0.001 ppm

Chlorine

50 ppm

Potassium

2 ppm

Fluorine

0.2 ppm

Sodium

50 ppm

Nitrate

2 ppm

Zinc

0.1 ppm

Sulfate

50 ppm

Heavy metals (lead)

0.1 ppm

Aluminum

10 µg/L

Microbial contamination

100 CFU/ml

Ammonium

0.2 ppm

Bacterial endotoxin

0.25 IU/ml Ultra-pure water for dialysis 0.03)

Table 2: Maximum Bacteriologic Levels

Parameter

Pure Water

Ultrapure dialysis fluid

Mikrobiyal kontaminasyon (CFU/ml)

<100

<0.1

Bakteriyel endotoksin (IU/ml)

<0.25

<0.03

Since local water sources cannot supply water to the required standard, all the hemodialysis centers must have a water system. The capacity and characteristics of the water system vary for each center according to the purpose and the characteristics of the local water source. It is recommended that the capacity should be 20-25% more than the calculated requirement when a water system is installed, as the need may increase over time and the production speed will decrease as the system gets older. 100 cfu/ml bacteria are allowed to be used in the water to prepare the dialysate. The nature of the water system should be determined by the use of the highest quality water and the situation where the local water supply is the worst.

Water system consists of water treatment and water distribution systems. The water treatment system includes the pre-treatment group and the main water treatment elements. In the pretreatment group, water is passed through a multimedia filter (sand filter, sediment filter) to remove particles first. Water is then filtered through the carbon filter to remove chloramine and chlorine, which are toxic in their contents. In the next step, the water is filtered through the softener to remove the calcium and magnesium content. With this softening process, it is aimed to extend the life of the reverse osmosis membranes and prolong their life. At the end of the pre-treatment group, the water is passed through a 5μm micro-particulate filter before the actual treatment and the reverse osmosis membranes are protected from damage by these particle filters. Most of the reverse osmosis membranes work most efficiently with the inlet water at 25 °C, the flow rate in the colder water decreases, and the hot water at 38 °C may cause damage to the membranes. Particularly when the pure water tank is used, it is distributed after an ultraviolet filter for bacterial cleaning and also passing through the endotoxin filter.

Purified water is stored either in a tank and distributed or directly distributed from the reverse osmosis device to the dialysis machines, and the unused water forms a closed circuit and returns to the tank or water treatment system. The water distribution circuit should, as far as possible, be made of non-metallic material which is not suitable for bacterial growth and should not be made of copper, zinc, galvanized metal and brass. Cross-linked PEX pipe or polyvinyl chloride is generally used for this purpose. Pipe diameters should be suitable for 1-2 m/s flow rate without requiring excessive pressure. The distribution circuit must not contain parts that can show stagnation in the water flow, such as closed end, branched pipelines and very large storage tank to avoid bacterial growth. In time, the performance of a water treatment system may decrease due to changes in the quality of the water supply, the life of one of the elements of the water system, and bacterial contamination. For this reason, quality control practices should be carried out including good follow-up and maintenance of water systems.