Hi Tanya,
In Nepal / Kathmandu anything is possible.
You could hit the jackpot and find your perfect home exactly as advertised on a housing website, or all could be a lie, just as long as you come and visit the house then they will try to talk you into renting it anyway. The former being a little less likely then the latter...
24 hours water is not that uncommon. There are vast areas in Kathmandu that suffer enormously from lack of drinking water, but at the same time there are equally vast areas that have never heard of any lack of water. It completely depends on the area where you're trying to rent. Personally I have a well in my backyard, and it has never run dry (yet).
24 hours electricity is usually a bit more tricky...
99% of the areas in Kathmandu valley suffer from loadshedding.
Loadshedding is scheduled, and if you know in which regime your area is located, you can know when electricity will go and when it will be coming back.
The schedule can be downloaded from the website of Nepals Electricity Authority; http://nea.org.np
Follow the 'Load Shedding Schedule' link from the homepage and you can download a schedule, and look up your group numbers plans (there are 7 groups in which your area can be located - just numbers without any preference in them, all have a different but equal load-shedding schedule).
Oh, and the PDF is in devanagari script, so you will have to study at least the numbers to understand the times (not too hard to do...)
So, no area has 24 hours electricity (temporary exceptions exist), and if 24 hours electricity is advertised, then usually it means that there is a backup, either by batteries or by generator. This could be a 64 Ampere backup which would allow you to run your whole building for hours and hours during load-shedding hours, but more likely (much more likely) is a simple battery backup which will allow you a simple reading light during load shedding hours, and can't power your PC or TV, let alone your refrigerator.
Wifi can be supplied by house owners, but they might want you to share in the costs of their 256 kbps internet connection, and in the bandwidth...
And security is not too expensive in Nepal, so many apartment complexes have a guard during night time. Then again... maybe the house owner will explain you he meant a lock on the front door with security... who knows...
My advise to you would be to first get yourself booked into a nice (or cheap if you prefer) hotel for the first couple of weeks, and from there start looking for a more permanent location for yourself. Don't rent a room or apartment over the Internet, for you will get much better deals and a better understanding of the location when you visit the place. Over the internet you don't smell the stink of a sewage plant nearby ...
Jorge.