I never wash any of my bikes with water.
Water, specially at high pressure out of a hose may get to places it shouldn't (i.e. bearings) and thus reduces the life expectancy of your bike.
Personally, I don't have a lot of space inside, and this works perfectly fine:
let your bike dry completely scrub off all bigger chunks of dirty with an old dry cloth use a cleaning agent (ideally something like WD40) for stains that don't come off easily degrease your chain, also using a bit of WD40 and some dry cloth possibly remove wheels from frame if you really wanna get everything off reassemble everything, grease movable parts using a little bit (!)
of chain oil or thicker grease (i.e. motorex)
if needed most importantly: repeat regularely , so your bike never becomes too flithy
bicycles.stackexchange.com/users/29822/dru87
I keep a piece of thick PVC foil, about 3×1 m in size which I spread on the floor in my corridor and put my bike on it (it has a kickstand so it can stand on its own).
I spread 4-5 sheets of newspaper just below the bike.
I take the chain off (which is easy since I have a master link) and clean it by shaking in a bottle of naphta.
I dust off all dried dirt from the frame using a cheap paintbrush (with a wooden handle so it doesn't scratch the frame).
What is left, I clean up with moist disposable paper towels.
If I'm in the mood, I clean the shock absorbers in the fork with a paper towel sprayed with WD-40.
After drying, I put the chain back on and lubricate it.
Most of the time, the dirt collected on the newspapers and the foil is completely dry so I can easily pour it over to the trash bin.
bicycles.stackexchange.com/users/28954/Michał Kosmulski
After a long bike tour through south east Asia (Thailand, Malaysia, and Indonesia totaling ~5000 km) we were flying back to NZ with our bikes.
NZ customs has very stringent requirements that no dirt/bugs/diseases comes in to the country on used sports gear, so we got the bikes sparkling clean by smuggling them up to our hotel room and putting them into the shower.
Nice low pressure, warm water.
Good drainage for the dust/dirt.
Soap and a flannel to clean up the frames.
No mess to clean up afterwards.
bicycles.stackexchange.com/users/23071/Penguino
In fact, using a cloth to wipe clean the bike dirt are quite eco-friendly.
You might use less water if doing it properly.
It also reduce the risk of splashing water into bearing,etc.
For heavy dirt like mud, first use gardening spray lightly spray to wet up dirt in order to remove them.
Just be careful when dumping the waste water, toilet bowl is a good idea compare to bathtub drain.
For greasy part, spray grease removal/solvent and use paper towel instead of cloth.
Don't feel bad about "saving the tree" on the paper towel.
Though cloth are "reusable" ,you will waste water and pouring those greasy dirt into your drainage, which is more harmful to the environment.
bicycles.stackexchange.com/users/26213/mootmoot
Put the bike on a bike repair stand inside of a room that doesn't have a carpet or any fancy hardwood floor covering. Put down a thick plastic sheet under the chain and cassette area.
Instead of plastic, you can use a few pieces of thick cardboard.
Clean the chain with 30 revolutions of the chain, back peddling, using a Park Tool cyclone or similar tool filled with Simple Green or another de-greasing product.
Keep the chain and cassette over the floor protection that you put down in step 2. Flush dirty contents of cyclone down the toilet.
Repeat steps 3 and 4.
6a.
Use small strips of cloth or "gear floss," soaked in de-greaser, to clean between the gears on the cassette.
Use a small brush, soaked in de-greaser, to clean the rest of the drive train.
6b.
Fill cyclone with warm water.
Repeat steps 3 and 4 using warm water instead of de-greaser.
Flush dirty water down toilet.6c.
Use dry cloth to dry the chain as best you can.
Mix a liberal amount of dish soap with water and use the mixture to fill up a spray bottle.
Fill another spray bottle with warm water alone.
Spray soap mixture onto bike to clean dirty parts of frame, rims, spokes, pedals, etc.
Wipe off with clean cloth.
Repeat step 8 with just the water spray.
Dry off the entire bike with clean cloth.
Remember to lube the chain before you ride the bike after cleaning.
bicycles.stackexchange.com/users/29872/Joe Heller
I would say it's probably easier / cleaner to take your bike to a friends house who has a garden or to a petrol station or car cleaning place (but don't use the jet wash on your bike).
I can't imagine trying to clean a bike in bathtub!
bicycles.stackexchange.com/users/1358/John Hunt
There are many sources describing how to wash your bike but all of them are for people who live outside town with a nice garden and a lot of space. Provably most of people live in small flats in a city block making it impossible to use these guides.  How can I wash a bike properly without going outside and having really small space?
How do I wash a bike indoors?
bicycles.stackexchange.com
<cleaning><indoor>
bicycles.stackexchange.com/questions/43272
bicycles.stackexchange.com/users/23458/kifli
To wash a bike indoors, something to cover the floor is needed. All major dirt should be scrubbed off. Stains can be removed with WD-40. A lot of water is not recommended as it can get into places it shouldn't. TheWiping down with a cloth is eco-friendly.  cahin should be degreased also with WD-40. Chain should be relubed. Any waste water should be discarded in the toilet. Place the bike in an area without carpet or sensitive flooring and protect the floor with a plastic sheet. Since water at pressure can damage bikes, using it sparingly can extend your bike's life. Let the bike dry and brush off loose dirt before wiping it down with a cleaning agent and cloth, wipes or paper towels. Dispose of waste water in the toilet rather than a sink or bathtub. Clean the chain with a degreaser in an enclosed chain cleaning tool, and use strips of cloth to clean between the gears of the cassette. Remember to lubricate moving parts after cleaning.
Place the bike in an area without carpet or sensitive flooring and protect the floor with a plastic sheet. Since water at pressure can damage bikes, using it sparingly can extend your bike's life. Let the bike dry and brush off loose dirt before wiping it down with a cleaning agent and cloth, wipes or paper towels. Dispose of waste water in the toilet rather than a sink or bathtub. Clean the chain with a degreaser in an enclosed chain cleaning tool, and use strips of cloth to clean between the gears of the cassette. Remember to lubricate moving parts after cleaning.