Collecting rainwater from the roof and eaves of your home can be a tremendously useful way to lower the amount of water your household uses (not to mention how much it pays for it). However, all the collected rainwater in the world is no use to anyone if you can't move it to where it needs to be, and larger collection systems are generally fitted with automated pumping mechanisms, particularly when used for potable running water.
If this is the kind of performance you need from your collection system, you have two ways of providing water pressure -- pressure pumps or a bladder tank. Each type of mechanism comes with its own advantages and disadvantages, so make sure to acquaint yourself with their properties before deciding which choice to invest in.
Pressure pumps are compact, versatile pieces of equipment that come in a variety of configurations. Some are fitted to the lid of the rainwater tank, or are fitted to the tank's outflow valve. Some submersible models are placed inside tanks, where they float just below the surface of the collected water. Pressure pumps contain sensors that can detect the pressure changes that occur when a water tap or valve is opened. The pump then switches on automatically, providing powerful and consistent water pressure for your pumping needs. When all taps and valves are closed, pumping ceases.
The small size and automated nature of pressure pumps makes them easy to install, and some models can be safely fitted without assistance from professional plumbers. They can be fitted to a variety of existing water collection systems without extensive modification and only require occasional inspection and maintenance. For smaller, low-pressure collections systems, such as those used for small-scale irrigation, pressure pumps can also be a much cheaper option than installing a bladder tank.
However, pressure pumps also come with a number of inherent drawbacks. Because they require time for the motors to wind up, there is often a noticeable lag between turning a tap on and water beginning to flow, which can be annoying when it comes to household use. Automated pressure pumps are also relatively complex pieces of equipment, and having aging or malfunctioning pumps repaired is often more expensive than simply replacing the whole pump.
A bladder tank is essentially a water storage tank and a pumping mechanism in a single self-contained unit; while they look ordinary enough from the outside, they contain internal bladders made from elastic rubber compounds. This bladder holds a large quantity of pressurised air, which is released into the tank when the outflow valve is opened. This provides immediate water pressure and flow.
Due to their simple construction and design principles, these tanks often last for many years with minimal oversight and maintenance, and there are few moving parts that can malfunction. The immediate pressure provided by the air bladder also eliminates pressure lag experienced by motorised pumps.
Standard bladder tanks have one overriding limitation, however; once the air bladder is emptied, the tank can no longer provide water pressure, and long periods of water usage can lead to your taps or hoses drying up unpredictably. You will be forced to wait until the bladder refills itself before full water pressure is restored. To get around this problem, you can purchase bladder tanks with small, integrated pumps that can temporarily take over for empty bladders, but these can be finicky and awkward to repair or replace in the event of a malfunction.