There is a very specific, hollow sound that haunts every hiker’s dreams. It’s that rhythmic slurp-gurgle coming from your backpack when your hydration bladder is down to its last half-inch of water. It usually happens just as you realise you’re still two hours from the car and the British sun has decided to turn the hills into a fan oven. And yes, yes, I know we whine about the cold all winter. But the heat can be just as problematic for a hiker.
I learnt this the hard way on the Crib Lem Spur. It was a September heatwave in 2023, one of those “Indian Summers” where the Carneddau mountains felt more like the High Sierra. I’d had to set off later in the day than I liked. By the time I parked up in Bethesda it was already approaching midday. Not ideal. There was also an incredibly long slog to even make it to the start of the scramble. By the time I made the start of the ridge itself, my tongue felt like a piece of sandpaper and I was staring down the long, dry walk back with not a great deal left in the bladder. It turns out, “winging it” is a poor hydration strategy when you’re hanging off a North Wales ridge.
The 1kg Per Litre Penalty
The “how much water” question is the ultimate hiker’s dilemma. On one hand, you don’t want to end up as a shrivelled raisin on a ridge line; on the other, water is deceptively heavy. One litre of water weighs exactly one kilogram. If you’re a “just in case” packer lugging four litres around, you’ve effectively added a 4kg lead weight to your shoulders and that’s far from ideal when you’re already contending with the heat.
That extra weight makes you work harder, which makes you sweat more, which… well, you see the problem. It’s a vicious, sweaty cycle. For a standard 4-6 hour summer hike in the UK, carrying two litres is usually the “Goldilocks Zone.” It’s enough to stay hydrated without feeling like you’re hauling a small toddler up a mountain.
Why the 500ml Rule Often Fails
You’ll see the “500ml per hour” rule cited everywhere, but the UK weather doesn’t follow rules. If it’s a breezy 15°C on a coastal path, you might barely touch your bottle. But add a steep 600m ascent like the approach to Crib Lem and a humid afternoon and you’ll be draining a litre before you’ve even reached the rock.
I’ve started “front loading” my hydration to get ahead of the game. I’ll down a good 500ml to 750ml with an electrolyte tab about an hour before I even lace up my boots at the car park. Think of it like filling the tank before a long drive; it means the water in your bag is your “reserve” rather than your “survival” stash.
The Filter Hack
If you want to move fast and light, you have to stop carrying all your water from the start. I’ve become a massive convert to the “filter hack.” Instead of carrying 4kg of fluids, I carry 1.5 litres and keep a tiny Lifestraw for back up. Do your research here though. Once I’d reached the top of Crib Lem Spur, I didn’t pass another stream. So this only works if you know you have water sources en route.
Electrolytes and the Forbidden Lemonade
If you start feeling “the mumbles” or find yourself staring blankly at your compass like it’s written in ancient Greek, you’re already behind the curve. Dehydration hits your brain way before you feel a dry mouth.
I always keep a spare electrolyte drink waiting in the car for the finish. It helps replace the salts you’ve sweated out (look for those white salt streaks on your top) and stops that post hike headache from ruining your evening.
Basically, for a solid summer day out, aim for two litres in the bag, a “front-loaded” pint before you start and a filter for emergencies. It’s the best way to make sure the only thing “slurping” at the end of the day is you at the pub in Bethesda.
