You'll need booster pump only if your tap pressure is not enough. 3-4 stage is enough.
Mecanical + carbon +
RO unit. You can add the fourth stage
DI part...
Or get as you said a kind of Mech+chem+chem+
ro+
di
In my case it's a kind of old
RODI unit 6 stages
Mech+chem+mech+
ro+antitaste+
di.
I plan to remove the antitase thing, I don't want to pay for this, so I'll get 5 stages:
mech+chem+chem+
ro+
di.
The chem part is important, as free chlorine kills the thin
ro membrane.
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