The world can be a turbulent place, and you may be bombarded by a variety of different sounds during the course of an average day. It can be some relief, therefore, to lay down at night and try to relax while the busy city winds down as well. Imagine how worried you would be, however, if you were to hear a strange hissing noise in the darkness and begin to fear the worst. Could this be a water leak, and if so, what should you do?
Unless you have a snake invasion, that telltale 'hiss' is likely to be the sound of pressurised water escaping from a tiny hole in a pipe. There will likely be a network of such pipes underneath the floorboards around you, and as they get older, they can sometimes develop a leak like this. One thing is for sure—you need to take action soon before it leads to a lot of damage.
Only Going to Get Worse
Whether you live in a single-family home or a block of flats, quick action is needed in order to contain the damage. You'll certainly want to avoid damage to the neighbour's place below if you do live in a flat, but you want to avoid costly damage to carpets and other infrastructure in your own home too. The hiss may only represent a trickle at the moment in relative terms, but the pipe could burst unexpectedly and lead to a proper emergency.
Do This Now
Begin by going into each bathroom or toilet and closing as many stop valves as you can. Go to the mains water supply and turn that off as well, so you can cut down the flow of water as much as possible. Don't be surprised if you can still hear the noise for a while after having taken this action, because there will likely be quite a bit of water left in the pipes.
Next, get on the phone and call your emergency plumber as soon as you can. They may ask you a few questions to help identify the complete issue but will be able to attend your property as soon as is practical to fix the issue. In the meantime, try to mitigate any damage, especially if you are fairly sure of the leak's location. And yes, if you happen to be above an apartment neighbour below, this may be the time for that awkward but necessary call.