Harvest rain water in a few water puts from house guttering, although its getting into spring.
Not sure about your setup at home,flat etc however get a cheap 300gpd system of fleabay. And produce. Its slow but good for a start before you upgrade system.
In all honesty
Di is not cost effective for you, take resin costs, leaflets, fuel etc you may as well get another job.
If you do use it for now as we all been their, tap should be very low pressure, it will be slow however prolong resisn life, get another vessel (cheap 2nd hand fleabay) makes it last longer.
When your tds starts to creep, shake the vessels.