First know for sure that where you are located uses chlorine and not chloramine in the water.
If chlorine, put water in a container(s) and put an air stone in the bottom to aerate the water and help off-gas the chlorine. Add a heater to match the tank temperature before using if necessary. 48hrs should be the minimum time to age the water, I prefer longer.
If you have chloramine in the water you have to use a checmical remover (or a special filter (actually you can use a filter for chlorine too)) and then age as above.
i have a 20 gal tub with charcoal and peet moss, some air pads underneath the charcoal and peet to draw the water through and a heater. whole thing cost me 30 to set up. i let the water sit about 36 to 48. seems to get the job done. This is for a 75 discus
I have a 120 and it usly sits around for about a month before i use it, and lasts about 2-3 months on my three tanks. there is a power head in it and a bubbler, a big bag of crushed coral in it and a heater.
I know its too much, im downgreading to a 80 gallon brute garvage can and upgrading to a drip auto ststem
1.) straight tap water and titrate the dose of strescoat or prime
2.) Get a trash bin (45-55 gal capacity) put an airstone and a heater (so that you can just use a pump and bring it back to the tank without worrying about temp fluctuation.
3.) Get a whole house filter to get rid of chlorine and heavy metals.
I did no. 1 for my 180 and had no problem, never did no. 2 since i do not have the time, space and spare pump. Now i am doing no. 3, large investment but for me it is not only for the fish, but for my house. I have about 1,300 gal of water, and i do not want to waste buying chemicals. (siphon on one side, and drain on the other side...