There is a gateway about two miles along a farm track I walk most weeks, and from December through to March it holds water the way a soup bowl holds soup. Last February I came at it in a hurry, near the dark end of an afternoon, and decided the tractor rut on the left looked shallower than it had the week before. It was not shallower. I went in over the ankle, both feet at once, and felt that first cold seam of water find the top of my sock and keep going. I stood in the middle of it and laughed at myself, because the boots I had on said waterproof on the box they came in, and I had believed the box.
The gateway taught me what the word actually covers
Waterproof, on a boot, is a claim about the material of the boot. It is not a claim about your leg. Everything I had been promised was still technically true while I stood there with two wet feet. The leather had not let water through. The membrane inside had not failed anywhere. Water had simply come in over the top, the way it comes into a bucket you push under a running tap, and no membrane ever made is going to win that argument with gravity.
Written down, that sounds obvious. It was not obvious to me in the moment. I think a lot of disappointment with gear lives in that gap. The thing does what it says. What it says is much narrower than what you quietly assumed, and nobody corrects you until you are standing in cold water working it out yourself.
Most of the water comes from above, not below
The second thing that took me two seasons to notice is that most of the water that has ever ended up in my boots did not come out of a puddle at all. It came down my legs. Long wet grass along a field margin at eight in the morning soaks the hems of your trousers, the fabric wicks, and the water runs down the outside of your sock and into the boot through the one opening every boot has. Rain does the same, only faster, and it does it all day.
I have finished a four mile loop with a damp left foot without once stepping in anything deeper than a tyre print. After that I started paying attention to where my trouser hem sat relative to the boot collar, which is a very unglamorous thing to think about, and it did more for dry feet than any amount of reproofing ever did. Gaiters help enormously and look ridiculous, and on a wet grass morning I have made my peace with looking ridiculous.
New boots and three year old boots fail in different places
A new boot in heavy rain usually does not leak so much as wet out. The outer material soaks up water and stops shedding it, the boot gets heavy, and your foot feels cold and clammy even though nothing has technically come through. That is a different problem from a leak and it has a different fix, which is keeping the outer treated so it sheds rather than drinks.
An older boot leaks properly, and in my experience it almost always leaks in the same place. Not out in the middle of the leather where you might expect wear. It goes along the crease that forms across the flex point where the boot bends with every step, or right down at the seam where the upper meets the sole. My oldest pair went at the crease. A cheap pair of rubber boots I keep by the back door split in exactly the same line. Thousands of bends in one narrow strip of material is what kills a boot, and once that crease has gone, no amount of proofing brings it back. I have tried. It buys you about a mile.
What I do now before a genuinely wet walk
I reproof the uppers far more often than the instructions suggest, because the instructions are written for someone who walks in summer. I lace properly all the way up so the collar closes around the ankle instead of gaping. I wear trousers over the outside of the boot rather than tucked in, which sounds like nothing and is not nothing, because tucked in turns your trouser leg into a funnel pointed straight at your sock.
And I carry a spare pair of socks in a plastic bag. That single habit has changed more wet days than any boot I have owned. Wet feet in themselves are survivable and even fairly pleasant if you are warm and moving. Wet feet when you have stopped, in a cold wind, an hour from the car, are how a nice afternoon turns into a miserable one. Dry socks at the halfway point resets the whole thing.
Drying is where boots actually go to die
My worst gear mistake had nothing to do with buying. I used to dry boots by the woodstove, close enough that they were warm to the touch when I picked them up. It felt efficient. It cooked them. The leather stiffened and then cracked along the flex line, the adhesive softened, and a pair that should have had years left in it went brittle across one winter. I was blaming the boot for being badly made right up until I noticed the pattern.
Now I pull the laces right out, take the insoles out and stand them separately, stuff the boots with newspaper, and leave them somewhere with moving air at room temperature, away from any direct heat and out of the sun. They take two days, sometimes three, which is much slower than anyone wants and is why the woodstove is so tempting. If I need boots the next morning I would rather put on a damp pair than a dead pair.
What I would tell someone standing in the shop
Buy for fit before anything else, because a boot that does not fit will not become a boot that fits, and no feature on the label compensates for a heel that lifts. Then treat the waterproof rating as one useful property among several rather than the whole reason for the purchase. Ask instead how the collar closes, how the tongue is joined to the upper, and whether the thing looks like it can be cleaned and re-treated rather than sealed up and thrown away.
Mostly, though, expect to manage water rather than defeat it. On a proper wet day on churned farm ground, everyone gets damp eventually. The people who look like they are enjoying it are not the ones with drier boots. They are the ones who planned for damp and packed for it.
I still walk that same track most weeks. I just go around the outside of the gateway now, along the fence line, where the ground is churned up but sits higher and drains. It took me one winter and one pair of soaked socks to learn a route that the farmer probably worked out when he was about nine years old.