The only need for water changes is nutrient / nitrate/nitrite removal otherwise unnecessary. Outside of that long as your GH and KH and mineral balance is good water it just the medium fish sit in. You can go months or longer without large changes or any water changes at all if your tank is balanced food vs waste accumulation.

If your concerned get seachem SAFE 10 USD. treats 60k gallons and kills out chlorines and nitrates. Then just clean filter lightly every 2 or 3 months.

The only reason I do water changes in a heavily stocked vertical 10 gallon is for needy plants and nutrient buildup causing algea of different types.

Water changes are for removal of nitrate and other salts. This keeps the fish healthy and water conditions clear. The specific frequency and amount of water changes depends on the water source, species, plants, and stocking level. A heavily planted, CO2 injected, lightly stocked tank using RO water to top off may only need a water change every few years. A overstocked goldfish tank might need 50% every other day.

When I was keeping my 125gallon tank in a drought prone area, I routinely used the water for my flowers and garden. Stuff I was going to water anyways and never worried about 50% water changes as it didn't impact my overall water usage.

I ran a 75g, 2x50g, and several smaller tanks for years. I was not wonderful about monthly water changes. I should think they will be okay skipping a month.

You could also try saving the water and filter it.

20 gallons is nothing. For context, watering a 1500 sqft lawn takes 1500 gallons of water.

I guess the data centers need it?

do you water any plants. can you reuse the water basically instead?

Water changes are not optional: clean water is a health and safety issue, and it's cruel not to.