I just recently bought this handheld shower and it works perfectly! It simply vaccuums water from a bucket and results in a steady stream of shower. It is battery powered and is rechargeable.

$24.99 (from $79.99)
Amazon.com

Click link below to buy:

Ivation Battery-Powered Handheld Portable Shower – Turns Water From Bucket/Basin/Sink Into Steady, Gentle Stream – Suitable for Indoor/Outdoor Use, Pet Washing, Car Washing, Camping, Baby Showering – Powered by Built-In Lithium 2200mAh Rechargeable Battery

I use it to bathe my baby since it has been difficult to bathe her in the tub at her current age; she is 5 months old – not old enough to sit up herself yet.

Pros:
Portable
Battery powered
Rechargeable thru USB to computer or USB plugged to outlet
Steady stream

Cons:
Noisy (not that it really bothers me)
Hook not that strong but sufficient if taking extra care of it

More info
In my experience, a fully charged battery lasts up to three baths (each 15-30 minutes)