Basically use dirty water, finely filter it, such that only things as big as phages remain. Put that liquid in a solution of bacteria you want to treat. Filter it again, repeat... In the end you should end up with some phage solution which specifically attacks the bacteria. If these phages don't work anymore, find new ones.
This reminds of the universal cure to disease being a bullet [1].
Phages are promising. That doesn’t mean they can’t hurt you [2].
The biggest hindrance is that the western process of developing and releasing new medicine is ill-suited for phage treatment.
The whole procedure of selecting a phage personalized for the patient and then growing it into a treatment is so slow the patient may die before it's ready. Works for chonic infections but not much else.
There are probably phage treatments that are not personalized: test susceptibility and then mail-order the treatment. That treatment:
- Would be very expensive to *produce* compared to most antibiotics. I emphasize *produce* because the price of antibiotics rarely reflect how much it costs to produce them. Compared to antibiotics, phage treatments have very low margins.
- Would work for a very limited percentage of patients (probably less than 10%). There are hundreds of phages for each bacteria species (yes, they're species-specific and sub-species-specific).
- Have a very *very* short shelf life, possibly a couple of days. So, no pharmacy or hospital can keep a sufficiently diverse supply of phages in store to treat most patients, possibly not even whole countries.