John as we spoke on the phone today you are in Carlisle with a tap TDS of 200 , what you want to know is what is the best option for you .
You have been recommended is if i remember is a 4021 RO System or possibly a 4040 RO system , You are working on your own and assume you are going to use 300-400 litres a day .
So ideally what you need to know is what is the best option for you and what experience do other lads have and what would they recommend and how much should you be expected to spend
Sorry if i hijacked your question as such just want to get the best advice from some other users for you , As i live in a soft water area my set is different .
And spending hundreds of pounds on a RO system is daunting when converting to WFP .