Watering a garden with
soapy water probably won't be a problem, but it depends on the
individual plants being hydrated (and whether you do it once or keep
doing it, thus letting problematic compounds build up in the soil).
The main problem from a
plant point of view would likely be salt/sodium and/or boron building
up. But bleach can also kill soil critters, causing long-term damage to
ecosystem health. Bar soap might increase the pH of your water, which
would only be a problem if you're watering acid-lovers like blueberries
or rhododendrons.
The more worrisome
problem would be the potential for fecal coliform from bathwater to
land on edibles that will be harvested soon (like leaf lettuce), making
you sick after you dine. That's why bathwater is often considered more
blackwater than greywater (unlike the effluent from your kitchen sink
or non-diaper laundry, which tends to be safer). To stay on the safe
side, it's better to apply these dicey types of liquid to ornamentals,
or to edibles that won't be harvested for several months.
The upshot? Read the
label of your cleaning products if you plan to toss them down the
drain. Then understand the difference between greywater and blackwater
and you'll be all set!