i get about 10.4 litres an hour or 250 litres per 24hours from my purefreedom 300gpd system, like you the water pressure is low but yours seems extremely low! How about a pressure gauge from ebay that fits on the end and see what pressure it is?
my pressure is low, but if i leave it on for several days in a row its fine filling the 1000ltr ibc, i use about 200 litres a day so its ok for me, you could get about 1000ltrs in 24 hours with a decent booster pump, like the one from ro man 24 7 one, though its not necessary for me.
mines for sale now anyway