Graphics created by @RSTheorycrafter1
I think the water filtration system is a really interesting piece of content for restricted accounts. About every twenty four hours on average, the system generates an item from a pool. I can reward uncut gems, onyx included, flowers for scarab hunting, 10,000-50,000 coins, a casket, soft clay, red sandstone, and golden dragon fruit seeds. There are a few less interesting items which can be retrieved from the system, but most of them are pretty easily acquired in the desert already. If Azzanadra’s quest is also completed, the water filtration system can also start rewarding elder troves, corresponding to the pontifex shadow ring tier, although that is less relevant to restricted ironmen. I think it is a little funny that this adds yet another way for a desert only ironman to acquire an onyx, or at least it would if it were not for the requirements to build the water filtration system. Bronze and silver bars can be smithed easily without leaving the desert, and buckets of sand can be gathered from implings, dust devils, or kalphites, but the challenging item is actually the big fishing net.
This item cannot be crafted with a loom, and must be bought or looted from the spawn in the fishing guild. The only shop locations are in Etceteria, Rellekka, Catherby, and Miscellania, none of which are in the desert. In the super strict ruleset, this would make the item impossible to acquire, but I think the water filtration device has a lot of potential on a slayer locked account, where the only items available to the player are those which are acquired from monsters on slayer tasks, or items gathered from processing the slayer monster drops. Stone spirits replace raw ore drops in RS3, with each stone spirit doubling one ore mined. It makes sense that a slayer locked player could keep half the ore mined from using stone spirits, which would allow the bronze and silver bars to be crafted. As previously mentioned, buckets of sand can be acquired from several different slayer monsters. Which just leaves the big fishing net, which could either be bought if shops are allowed, or looted if item spawns are allowed, although that might require some lamping or fishing without keeping the actual fish. Either way, the water filtration system opens up some great loot for the slayer drop locked account, with a big one being granite for granite crab pouches. The temptation to start a slayer drop locked account continues to grow stronger.