I am going to assume you have the more recent Saint brakes, BR-M820.
A true blockage in a ceramic-piston Shimano brake such as yours that occurs when fluid should be able to flow through as per the bleed procedure is usually a sign that a piece of the ceramic piston has broken off. This is often accompanied by erratic brake feel or function being the symptom that had you bleeding it in the first place, such as piston retraction issues or difficulty with getting the brake to gap evenly and stay that way as it should.
It's of course possible that something else got in there and is causing the blockage, but the broken piston scenario is relatively common compared to that and you have one of the brakes it applies to.
Don't put water in your brake on purpose. Shimano brakes are able to survive minor water contamination of the sort that could happen unintentionally, and usually replacing all the fluid is sufficient to make the brake function well in those cases. I don't have concerns that hot water alone would ruin anything, but you need to get it completely out of there, ideally with compressed air on the hose and lever end (since this lever isn't very able to be disassembled) and in this case piston disassembly on the caliper end, see below.
Usually the thing I do with potential/probable ceramic piston cracking issues on the higher end brakes such as this is take the caliper off completely, drain it best as possible, split the caliper, and then pop the pistons out with an air gun (they pop out readily when the air gun is at one of the fluid entry points and you plug the other with your thumb). Most of the time the way this goes is you see a piece of broken white piston floating around, which means the whole thing is shot since there are no replacements. In theory you could also find some other contaminant, which is how you could fix the brake if so, but you probably won't. Then either replace or clean and re-assemble the caliper and put it all back together. The pistons re-install with hand force after thoroughly cleaning everything and lubricating the bore with the mineral oil you'll be using for the bleed.
If you disconnect the caliper hose attachment and open the lever bleed port to see if flow-through occurs, that's how you would test whether the block is in the caliper or not. It probably is. If it isn't, you could then do other tests to see whether it's the hose or the lever that fluid isn't flowing through.
All of this is fairly advanced hydraulic brake shenanigans, but as long as you're very careful when handling the ceramic pistons and you only use appropriate oil and cleaners (isopropyl alcohol or ethanol would be what I'd limit it to), you're safe to mess with it. Most of the time the direction this goes is replacement of the caliper.
Some mechanics I've known have been willing to cannibalize ceramic pistons from dead same-model Shimano calipers to make a good one out of two bad ones. I know of a number of cases where this has worked without issue, and none where it's been tried and hasn't worked. I personally am not willing to do it on someone else's bike for fear that a piston might look dimensionally compatible but not be for batch-related reasons etc., since they're not intended by Shimano to be a replaceable part. That said, the chance of issues is probably quite small if it seems to be functioning normally.