You might be searching for a pump that operates on 12 V and gives an output of above 240L/H then this could be the best choice for your project.

This Ultra-Quiet DC 12V 3M 240L/H Brushless Submersible Water Pump is a low-cost, small size Submersible Pump. It can take up to 240 liters per hour with a very low current consumption from 300mA. Just connect the tube pipe to the motor outlet, submerge it in water, and power it. The black color pump comes with a heavy-duty cable and a 5mm DC female jack at the end to connect directly to the 12V power supply.  It is widely used in prototype projects as well as for decoration purposes.

Caution:

Make sure that the water level is always higher than the motor. The dry run may damage the motor due to heating and it will also produce noise.

Features: 

• Super long working life(more than 30000 hours); Adopt high-performance ceramic shaft.
  
• The axis is enclosed with static sealing, not dynamic, which can avoid leaking problems.
• Amphibious design; Submersible installation and entirely waterproof.
• low consumption; low noise(less than 35db),  used in computer cooling system, Garden fountain.
• Used in Aquarium, car cooling, humidifier, air conditioner, other cooling and circulation systems.

Package Includes:

1 x Ultra-Quiet DC 12V 3M 240L/H Brushless Submersible Water Pump