Resupply
Making Water
Rainwater, dehumidifiers, atmospheric water generators and field methods. What each one actually yields, what it costs per gallon, and what your state law says about the cheapest one.
Storage runs out. That’s the whole reason this section exists.
A two-week supply is a two-week supply, and if the interruption lasts longer than the shelf you filled, the question stops being how much you kept and becomes how much you can produce. There are four honest answers, and they differ from each other by more than an order of magnitude in yield.
Rain is the cheapest water you will ever get
A thousand square feet of roof catches roughly 600 gallons from a single inch of rain. Not a season. One inch, one storm.
That number surprises people, and it reframes what a rain barrel is. A single 55-gallon barrel on one downspout is not a system, it’s a sample. The roof is the collector, and the roof is enormous. Whatever you can store is the actual limit, which is why the yield calculation and the storage calculation belong together.
Rainwater is also the least contaminated source on this list before it lands. What it picks up comes from the roof: asphalt granules, bird droppings, whatever settled since the last storm. A first-flush diverter throws away the dirtiest opening gallons and solves most of it. Drinking it still requires treatment, and roof material matters, but the starting point is far cleaner than a creek.
The catch is regulatory, and it’s the most misunderstood topic in this entire subject.
| Method | Typical yield | What it needs | Treatment | Verdict |
|---|---|---|---|---|
| Rainwater, 1,000 sq ft roof | About 600 gal per inch of rain | Gutters, a diverter, storage | Filter and disinfect | Highest yield by far |
| Dehumidifier you own | A few gallons a day when humid | Power, humid air | Disinfect | Free if you have one |
| Atmospheric generator, 45% RH | A fraction of the rated output | Power, moderate humidity | Usually built in | Check your own humidity |
| Atmospheric generator, 30% RH | Close to nothing | Full power draw regardless | Not applicable | Bad buy in dry climates |
| Solar still | Under a gallon a day | Sunlight, a tarp, a pit | Already distilled | A technique, not a supply |
The legal question, briefly
Collecting rainwater is legal in every US state. What varies is whether there are conditions attached.
The belief that it’s banned traces almost entirely to Colorado, which restricted it for over a century under prior appropriation water rights, and which changed the law in 2016 to allow residential rain barrels. The ban people remember is gone. The story outlived it by a decade and is still repeated on preparedness sites that never checked.
Several states do regulate collection: volume caps, permit requirements above a threshold, rules on what collected water may be used for. Several others actively subsidize it with rebates. The details are specific enough that a general answer is worthless, so we keep a page per state with the current statute and the date it was last verified.
Water from air
Air holds water, and you can take it out. The question is how much, and the answer depends almost entirely on humidity in a way the industry does not advertise.
A dehumidifier you already own is the cheapest version. In a humid basement it produces real quantities, and it costs only electricity. The water is distilled-adjacent and picks up whatever is on the coils and in the bucket, so it needs treatment before drinking. As a resupply method during a grid-up water outage, which is more common than people expect, it’s genuinely useful.
An atmospheric water generator is the purpose-built version, and it’s where the honest numbers matter most. Every manufacturer quotes output at roughly 80% relative humidity and 86°F, which is a summer day in Florida. At 40% humidity the same machine produces a fraction of that. At 30% many produce almost nothing while still drawing full power.
That’s not a scandal, it’s physics, and it’s the single fact that decides whether one of these belongs in your plan. It’s also the fact nobody selling them puts on the box. If you live somewhere dry, an AWG is a bad purchase and the arithmetic says so plainly.
A solar still needs no power and produces very little. Field manuals include it because it works with a tarp and a hole, not because it feeds a household. Treat it as a survival technique, not a supply.
What things actually yield
Ranked by gallons per day for a typical household setup, best first:
Rainwater, in a wet month, produces more than you can store. Rainwater in a drought produces nothing, which is the pattern that makes storage and collection complementary rather than alternatives.
A dehumidifier in a humid climate produces a few gallons a day for the cost of running it. An atmospheric water generator produces somewhere between that and nothing, entirely depending on your local humidity. A solar still produces a fraction of a gallon and consumes a day of sunlight to do it.
Every one of these needs treatment before it becomes drinking water. Collection and purification are two different problems, and finishing the first one does not finish the second.
Where to start
Find out what your roof yields, because it’s free, it’s the largest number available to you, and it costs about thirty seconds to calculate. Then check what your state allows before you buy anything. Then, if you live somewhere humid, work out what a dehumidifier or an AWG would actually give you at your real conditions rather than the number on the box.