Maybe you and your boyfriend, he and mom should sit down and discuss WHAT exactly the problem is and why he is coming down on YOU about it! Tell him point blank, I don't know WHY you are blaming me for doing so much laundry and WHY the water bill is so high, but this has to stop and we need to find a better solution. And then explain how you feel about this situation. The ONLY way he is going to know, is if you TALK to him! Tell him you want to be reasonable and that every time you two save money to try to move out, something happens that is YOUR fault and you have to pay out even more, so you aren't saving anything.
I learned a long time ago, problems DON'T go away if you don't talk about them. I know people who would get mad at me and then not tell me what was going on! I'm not a freaking mind reader! So you have to tell me what I said or did to know! It's the same with other people. I got to a point where I told people, HOW am I supposed to know what is going on or what you want me to do, if you don't communicate!?!
Just yesterday, I had to remind my mom about this. She has a very bad habit of not telling me stuff and then expecting me to know. Which frustrates me to no end, because my dad and I DO communicate daily!
Just have a sit down, write down what he thinks, and maybe ask if he likes doing the laundry for everyone. Who knows? Maybe it's fun for him!