I have a six stage RO/DI (Reverse Osmosis and De-ionisation) filter setup I just installed a few weeks ago. There's a split line in the middle of the system and a presure tank. The water passes through three filters, then the RO filter and then either goes into the 3 gal storage tank and then out through the carbon filter into a tap on the sink for drinking/brewing/freshwater aquarium use (99% pure); or I can use a seperate tap to pass it from the RO filter into the De-Ionisation filter then out through a seperate tube for saltwater aquarium use (99.9% pure). It's not reccomended to drink DI water because you've taken TOO much out of the water, but Marine Aquariums want water as pure as possible.
From my understanding, using DI water for brewing wouldn't be worth it as the brewing process add's back plenty of adjuncts and proteins and contaminants so it defeats the purpose. Likewise not advised for Freshwater tanks as it strips out the beneficial minerals the plants and animals need. Marine tanks are different as you are mixing up saltwater with a carefully balanced mix so you want ultra pure so you know exactly whats going in.
It's a complicated setup ad takes up a lot of room under the sink but gives me pure water for drinking for the family, pure water for brewing and carbonation for soft drinks, and for topping up the freshwater tank and then ultra pure water for my saltwater tank setup.
If you're not keeping fish, better to skip the last DI filter setup and go straight RO. My setup was AU$300 plus additional international shipping (purchased from US through eBay). Just shy of $400 all up. Local sellers where considerably more expensive. RO setup on it's own is a bit cheaper.
I will point out that an RO filter slows the passage of water quite a bit. You need to have a pressurised storage tank as part of the setup. The filter system keeps the tank permanently topped up and the tap draws from that. My system has a 3.2 Gal/12 litre tank. That means a standard brew for a 19l corny or for 23L worth of bottles, will drain the tank fully and you have to wait for it to refill to finish filling for the brew. Depending on the rating of your RO filter it can take some time to refill the tank. Mines rated at 100 gal/378 litres per day so a little under an hour to refill the tank. It just means that filling your kettle or fermenter can take a while and is a two step process.
Additionally, bear in mind replacement cost for filters - RO should be done every 2 years depending on usage. The other filters every 12 months. You can source cheap filters online, and the fittings are an international standard so any filter brand should fit. But four to five filters every 12-24 months can add up. Bulk buying the filters is a good option to invesitgate.
Final consideration is your home water pressure. If it's too low you need a booster pump to push it through tthe filter, Too high and you need a pressure control valve to slow it down.
It's a bit complicated and there'ssome testing and research before deciding exactly what you want, but once you have that, installation is easy (did it all myself). An RO system does takle up a LOT of space under the sink though, because of the storage tank.
One thing that KL should consider when stocking these is that, technically, I think your supposed to get them fitted by a licenced plumber? The process is actually really easy, and only required drilling a single drain hole in the waste pipe and a hole for the tap in the sink, everything else was push in fittings similar to the duotight fittings. But if the local regs state you need a plumber to install, that's an additional cost on the purchaser. Buying from a local water filter company often includes installation in the price.
Previous brews I did just using a standard 3 stage water filter (not RO) or even just using tap water (our previous house only had 3 stage, and I did two brews in the new place before installing the new setup) I honestly didn;t notice that much different. A three or four stage filter purifies your water a lot and is probably enough for the average user. The RO is an extra stage for those who really want to go pure. Personally, I wouldn't have bothered if I didn't need the ultra pure RO/DI water for my reef aquarium. I would have just got a cheaper, smaller and simpler 3 stage filter.
For the chlorine why not try Campden tablets to strip chlorine and leaves minerals
