RO question/advice

[hillegom]

13 ppm is typical for the lower mainland. It will vary a little, depending on the season.
Most ro systems typically "waste" 4 gal for every one they produce. You can buy more efficient ones, but I think the membranes won't last as long.
How many gpd (gal per day) does the one from costco produce? If its 25 gpd, then one gal per hour, 25 divided by 24hrs is about what you are getting.
That is assuming a water pressure of at least 60 psi in your house and room temp water going through the filters.
If you want to decrease your TDS to 0 then you need to add a DI filter.