My try

The downward force of the water is sufficient to remove any exudate, contamination, necrotic tissue etc. This removes the need to use swabs which can do more damage to the wound. It doesn't always need to be sterile water or saline but can be in some cases depending on the wound. It can be done by the use of a showerhead (ensuring the pressure is below a certain level) or syringe, but the water temperature has to be maintained about body temperature.

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Note added at 3 days 23 hrs (2020-08-17 12:30:18 GMT)
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With some more digging, I think this may relate to 'ducho terapia' - it's outlined here https://sites.google.com/site/metodosenenfermeria/metodos-de... . It refers to cleaning (in this case, diabetic wounds) with either a flask held high (by a drip stand) connected to a shower head, a flask with holes pierced in it, or a traditional shower. It is used where the wounds are larger. In the case of smaller wounds, a syringe is used 'jeringa y aguja' instead. Both have the same goal, but the techniques are different. So, I would suggest the translation should be 'downward irrigation with gentle shower to clean the wound'. As Chema Nieto points out, it may not be downwards, but if you're brave enough (!) have a look at the photographs that show the procedure to see if this helps to explain what is happening.