You have multiple people working together, buy water filters and setup dew collectors asap. in my single player game I have 8 dew collectors already by day 9 or so. Course you'd need alot more with that many people. They need to just make higher tiers of it I feel, that produce more water over the same time using the same 2x2 space. Maybe start with the base Dew collector, then you can use a upgrading tool like claw hammer with enough materials to tier it up so it produces more faster and has more storage slots. There is a mod on nexus that actually sort of does this already. it lets you combine 3 into 1 which generates packages of 3 water per slot 15% faster than the base one would gen 1. (as its 3 in 1 basically), then you can 3 of these triple dew collectors and turn it into one that generates packs of 9 water per slot, all in the same 2x2 space. This would help in MP as your going to need alot of purifiers for the people. Heres the mod maybe it'll help at least on the space needed, and it does make them produce 15% faster than normal as well when combined.
https://www.nexusmods.com/7daystodie/mods/2986
You should know by now that TFP doesn't like the player to have choice, as they keep taking away more sandbox elements each alpha, it all started really with stealth being made so bad and poi's behind designed to be anti-stealth, then you have digging zombies, so you can't make a underground base. Also don't say it was done so you can't avoid horde night, go on any moderate sized poi and knock the stairs out and you can pretty much avoid any bloodmoon horde that way. They just wanted to remove choice from the player which is pretty much their motto these days. TFP seems to want to force us to play a certain way and will change things to do so. Most recent being the magazines. In single player its fine, as you'll be out looting anyway, but it really screws with multiplayer as you can't just be the stay at home builder or miner, you have to go out and loot now to get magazines and water. Its the opposite of the stat system, the stat system is aweful for single player, but works fine in MP as you can have your community str dude for mining etc, but when your in single player you have to do everything yourself and the stat system just forms 5 level gates, instead of a16.4's single level gate.