When it comes to pre-conditioning, I think I just may 'win' (or lose!).
I live in the country and have a well. I don't have to deal with chlorine or chloramines. There was a time that I simply got a garden hose adapter for the sink and indexed the faucets for the proper temperature. I'd insert the siphon hose into the garden hose and siphon out to the front lawn. Then hook up the hose, set the faucet handles and refill - no muss, no fuss.
Then I discovered I had HIGH NITRATES (60-80ppm) IN MY WELL WATER
. You see I had some Platys that came with a 'payload', but the fry would seem to have a very short life span for no apparent reason. This lead to the testing and discovery of high nitrates. The most likely reason for the high nitrates is a 95 acre farmers field across the road that gets ample amounts of organic and chemical fertilizers.
So this began my quest to reduce tank generated nitrates as well as obtain water suitable for water changes. Purchased bottled water at $1 a gallon really adds up!
1) I bought an API Tap Water Filter to make deionized (DI) water. DI water is treated with Seachem Replenish for minerals and Neutral/Alkaline Regulators for pH. For my water, I only get about 50g for each $25 filter cartridge.
2) I setup a 10g tank in the garage and used Fluval Lab Series Nitrate Remover (FNR) to remove nitrates from my well water. FNR is a synthetic resin that adsorbs nitrates and is regenerated/reused with salt water.
3) I collect and use rain water (treated much like DI water for minerals and pH).
I would typically mix FNR with DI or rain water 50/50 to produce a 10-15g weekly water change.
For reducing tank generated nitrates:
-> Developed a DIY denitrate filter
but even with copious amounts of Seachem Stability, I could not seem to culture the anaerobic bacteria to complete the N2 cycle and convert nitrates to nitrogen gas. (now discontinued).
-> Added several bunches of Anacharis plants.
-> Minimized feeding.
-> Aggressive gravel siphoning and filter maintenance.
-> Experimented using Seachem Purigen to remove dissolved organics before they are broken down, eventually to nitrates.
-> Switched from gravel to deep [pool filter] sand.
-> Added an Aquaclear 70 filter with an Aquaclear 20 impeller for a trickle flow through the Matrix/De*Nitrate bio-media mix... While my other AC70 just uses foam/pads/floss for mechanical and the media is changed regularly.
-> Experimenting with Aquabella
So that's my story. A fair amount of effort to combat high nitrates in my source water. I ruled out an RO/DI system for the house. The cost would be increased as due to pressure, I would need an additional pump to get water through the membrane. Also 4 gallons of waste water for each gallon or RO water just seems crazy to me. Also, even with treating the DI water, based on general fish behavior, when I've attempted to use it alone without mixing my FNR filtered water*, it seems something is missing. So I continue 'making' water to use for water changes.
*With winter coming, for FNR filtered water, I discontinued my 10g setup in the garage for a 29H setup in the basement.
...and so, the saga continues.