General Overview
Outcast Silver Raiders is obviously an OSR game, like all OSR rulesets made by handsome and clever people its abbreviation is "OSR". It is designed to be a gritty horror version of an OSR game (or at least horror adjacent and full of horror aesthetics). Players are not heroes or adventurers but explicitly weirdos who have been outcast from society and live by killing and plundering during the dark ages. Towns are not likely to be welcoming to these people unless they have a temporary need of a band of unhinged violent lunatics. It being the dark ages, that is often common.
A Mechanic that works really well
Magic is supposed to be evil and awful, but if you want to have a magician class then you have to give them something to do during most games. Outcast Silver Raiders solves this by separating magic into two bits:
Blood Magic, a thing PC sorcerers do where they lose HP to either heal a non-sorcerer ally, give an ally a bonus, or injure an opponent. Simple, quick, gives the characters something to help with during fights or dungeoneering without needing a complex spell list.
This of course leaves out making magic feel weird and dangerous and occult. This is where demonic rituals come in, they do al the "magic is weird and terrifying" stuff. They take special ingredients, a long time to set up (66 minutes), special steps you have to learn (and like Carcosa before it are often awful), and can technically be done by any character.
A detail that lifts above its weight
Flat out listing that players have a duty to not look at their phone at the table and hammering home there is no such thing as multitasking. I know this is "old man yells at cloud" of me, but don't use a phone at the table. If its not important enough to leave the table and/or duck out of the room for then it isn't important.
For a game with horror themes this is even more important, you can't build a sense of dread or horror if every 5 seconds one or more players is looking up and going "sorry, can you repeat that?" while side-eyeing their phone.
Constructive Feedback
I get scarcity dice are a thing that are popular. Even if I think they are overused, its a valid design choice and I won't comment on that.
BUT
Please make them rational. IF you going to bother tracking water at all, it should be because you want that to be an immersive thing. You need to find water as a priority when traveling.
A single water skin, taking a single inventory slot has a usage die of a d8. On a 1 or 2 that drops to a d6, then to a d4, then finally done.
Even if you are terribly unlucky it becomes automatic to carry three days worth of water in a single waterskin. If you aren't the most unlucky person ever, then on average you can make it over a week between stops at an oasis or well.
Water is the single most difficult thing to pack while traveling and also the most important. It is why wars are fought over access to watering holes in the desert.
An average peasant with a backpack (10 STR) can carry (on average rolls) 7 weeks of food and water on their person without being encumbered. A group of peasants will average out and thus remain at about 7 weeks (some will roll poorly, some well).
Either don't track food and water, or make food and water matter. Make it something fights break out over and grim choices are made if you want this to be a gritty game.