You can use industrial strength Velcro as a holder. I find this works best and is the safest method out there. Plus, you can several feet of it for pretty cheap! If you don't want Velcro, I've also been able to use suction cups+zip ties, but this method is more of a pain than others. However, it's still an option if you wish to go super cheap. You can also get the metal pet store bottle holders. These do have risks associated with them if your hamster climbs, but as long as they don't, I wouldn't be too concerned over it. There are also bottles made specifically for aquariums that will stick to glass/plastic, so that's worth looking into if you can. Homemade bottle holders are also an option, but are a little more time consuming than simply buying them, but again, this is another good option. Lastly, you could simply use a bowl. A shallow reptile dish is best for this purpose
Good luck finding a holder
https://www.amazon.com/gp/aw/d/B00TC...dlL&ref=plSrch
https://www.amazon.com/gp/aw/d/B06XG...mRL&ref=plSrch