I was thinking to install indoor cameras in the common areas. I am renting a room in my own apartment and I realize that my guests are turning on the water heater tank.
There is hot water for all of us if we take shower that last no more than 15 minutes. The first few days we didn’t have any water left because one of the guest in the morning took half an hour shower. We explained the situation to him and it seems that everything was in order. But this morning I heard one of my guest turning the water heater tank on, I don’t think he realized I am in my bedroom and I can hear him.
What should I do to avoid this kind of situation in the future, what about installing cameras in the common area, I think if they know there is a camera they will not do any of the things that they are not suppose to do.
No, never indoors. Even if you inform them of the cameras, only trouble can come of it.
I don’t understand the question. If the water heater is off, there’s no hot water surely? If I was paying for accommodation, I’d expect to be ‘allowed’ to have a shower of more than fifteen minutes, especially if on vacation. That is, unless there’s a water conservation issue of some sort - which doesn’t seem to be the case here.
Rather than get cameras (and I agree with @Colorado) it would be better to change your hot water system so that you don’t have to impose restrictions. I shower as quickly as I can but with long hair it can take more than fifteen minutes. My other half, on the other hand, can take forever and he has hardly no hair 
the water heater tank gets hot during the night and then we have hot water for the rest of the day. We can turn on the heater tank during the day if there is no water, but it will be more expensive. We can’t change our hot water system. We usually have short time guests, so it is not a problem in that case we charge more because we take in account that some people want long shower
In the current case we have long time guests and the rent for them is a lot cheaper. The electricity bill of course it is not included (I am not that stupid )and it will be sharing among all the people living in the house. So they will have to pay more if the electricity bill will be more expensive. If everybody start having long shower, doing 10 washing machine a day and keep the heating at 86F the bill will be very expensive of course not everybody will be happy. Of course they can have very long shower if they want, they can move to the hotel nearby where they will be charged 10 times more,but they will have plenty of water. If they don’t agree with the house rule of water preservation in my home they are free to leave the accommodation the same day.
When I travel I need to stay in a very warm place for health reason and for this reason I book always an hotel, I am not expecting that a private house will accommodate my needs.
why?which kind of trouble?
In that case, I suspect that you need to raise your prices. Airbnb’s advertising (which guests tend to believe) is that their accommodation is a ‘home away from home’. They expect at least the same basic facilities that they get in their own place. (Unfortunate, but true). If a local hotel charges ten time more than your rental, then it wouldn’t be unrealistic to raise your prices.
Do you have a note/sign/label in the bathroom / shower area, or do you only list it in your rules? A friendly reminder may go a long way…
I have two small signs in our rental space’s bathroom that kindly asks guests to use water sparingly. 99% of people respect the request.
We truck water to the house so have to be mindful of usage.
most of their own place is with mum and dad that pay all the bills for them.so they really don’t have a clue what is like having to pay bills. I just need to educate them
Thank you for your advise, I will hang a note in the shower area
This is a house rule? If so, then sit them down and tell them they are not to tamper with the hot water. I sleep 6 guests and there is no way they all could have a hot shower over 15 minutes each (back to back). We considered getting a larger tank but then my partner said he was afraid guests may run the well dry if they are just staying in there because they have endless water. One of the showers has body jets, so they could easily go through lots of water.
Explain to them that you accepted their reservation with the understanding that they are going to live like the other members of the household. How long term are these guests?
Have you advised potential guests before booking re the restricted access to hot water? Where is your apartment ?
Can you simply lock the area where the switch is? Or put a lock on the switch?
I had thought about getting a fancy showerhead with all kinds of features. Then realized that would just be inviting them to stay in the shower longer. I want them in and out as fast as possible. So I kept it pretty no frills.
it was not in the house rule because we didn’t bother for short term guests. They are staying for 4 months so this time is different. We talked to them and they agreed, I guess it also my fault for not having taking in account this. We did have in the past long term guests but nobody stayed ages under the shower
I don’t know how many others are in the house, but it isn’t fair to the rest of the people. It’s not like they only have 5 minutes…it’s 15 minutes.
@Mearns set his tankless water heater up with a timer. It goes ice cold at four minutes. That gets them out fast.
I am on rainwater catchment here in Hawaii. It’s all over my rules that they need to conserve. I always always greet the guest in person and show them the tank and ask for mindfulness with water. It works like a charm. I cannot have someone take a 15 minute shower here. It doesn’t need to be army but it can’t be 15. Most guests are honestly so good now. I never have the problems I used to since showing them in personally and reiterating about the water again. (Even though there are signs too.)
What happens if a guest needs a shower and there is no hot water? It’s not right to deny them hot water. If another guest has used it all, you need to provide this most basic utility.
the other guest is his girlfriend. She will have to deal with him, it is not my business if his boyfriend wasted all the hot water
I have this exact problem; a water tank that heats a fixed amount of water at night. It normally lasts all day and doesn’t run out.
It’s never been an issue except one time, when I had a guest who liked to have long showers morning and nighttime. the worst was when I got a message at 9.15 am saying there was no hot water. For it to run out so early in the day, I knew then that someone had been in the shower for approximately 45 minutes. I replied there was a fixed amount of hot water but got in a taxi from work to find out what was going on.
I arrived home to find the heating on full blast With the windows open, the hot water heater turned on and both guests out. You can imagine how angry I was …
I’m a bit slow tonight 
I was wondering what difference it makes that they are long term guests and finally realised that you’ve given them a discount. How did you calculate the discounted rate? It seems that the discounted price wasn’t correctly calculated. I know it doesn’t help with these guests but for future, it might be a good idea to make sure that you still get your required profit margin when you discount.