Tap water should be fine
The cage size goes by continuous floor area. So it's ok to have two cages attached as long as one is big enough. The recommended minimum in the US is about 450 square inches continuous floor space. That's about the size of a Duna Multy cage (70cm by 40cm). You wouldn't want anything smaller than that for a Syrian - they need a base that's deep enough for plenty of substrate for digging, and house and toys large enough (rat sized toys and tunnels are best for Syrians).
It's so they can have space for normal behaviours like digging, foraging and exploring - especially at night when they're most active.
The equivalent to the Duna Multy in the US is something like this FOP cage from Abbaseed. The top one on the page.
HAMSTER CAGES
Personally I'd go for something a little bit bigger than that - heightwise it only fits a 9" wheel I think. They do much better with one larger cage than two joined together - even if one is big enough.
A lot of people in the US make bin cages as good sized cages are hard to find and usually expensive. The alternative is a diy cage, a detolf or a glass tank (a 40 gallon breeder is popular for a Syrian).
Pet shops will sell anything unfortunately - there is no legislation as to what cage size they sell, so it comes down to animal welfare organisations to recommend suitable habitats for hamsters.
Some people have taken a cage back for a refund saying it's too small. The Ovo is very cute but not really suitable for a hamster cage. The Twist is too small as well and you'd have difficulty fitting a Syrian sized wheel in. Any wheel smaller than 8" diameter is bad for a hamster - they need a wheel big enough they can run with a straight back - or they can get back pain and problems. Often they just stop using it if it's too small.
This is a good cage for a Syrian, but it's expensive. The Marchioro Goran 82 (not the 72)
https://www.petmountain.com/product/...-rat-cage.html
Petco have dollar per gallon sales regularly and you can get a 40 gallon tank for $40 during the sales.
Or you can get a detolf for $40 (an Ikea glass cabinet tipped on its side with the door left off - it needs a lid making though, so some diy).
https://www.google.co.uk/search?q=ha...w=1525&bih=678
I would definitely look at asking the pet shop to take it back for a refund and get something else - so you have a happy, healthy hammy. Their behaviour changes noticeably when they're in a bigger cage with more places to go and things to do
The basics are 4 to 6" of substrate, a house/hide big enough to build a big nest in, somewhere dark to retreat to to feel safe (this can be the house if you put a bendy bridge over the door so it's dark inside), some kind of level or platform to sit under and climb onto. They like sitting on a shelf. Hidey places, tunnels, tubes and other floor toys.
This is our Syrian's cage set up
Attachment 43508
As for the blood, just wondering if there is anything he could catch himself on - a sharp bit of plastic or something?