hyaaaooo ...eye roll...
I would ask them to do the math about how much 15 hours without water is worth in percentages of what they have paid for the accommodation taking into consideration the following variables:
- 8 out of 15 hours was sleeping time so they were out of water for only 7 hours out of their xx hours long stay
- Besides the water, the accommodation price also includes: gas, electricity, A/C, WIFI, TV, xx m2 of the property, heating, furniture and beds, beddings and linens, kitchen with all utensils, soap and toiletries, parking spot if any... etc, whatever you provide including toilet paper
Then wait 🙂