Question
I am planning a system where I am going to catch runoff water into a 1500gal plastic tank. I plan on connecting a in line pump to operate both an outdoor shower head as well as a faucet which I will use primarily to run a sprinkler(1 or 2 at a time) for irrigating a 30'x60' garden and lawn. The pump will be fed by gravity from the tank.  I am thinking that a shallow well pump with a 5gal or so tank will work.  I have seen ones that have psi ranges from 30-50.  I would like to go a bit higher in the psi range if I could just due to the distance from the pump I will be watering. My questions are: Is it ok for this type of pump to be gravity fed like that or do you have a better suggestion for pump type.  Can you recommend a  reasonably priced pump for this application?

Answer
Hi Bryan

It sounds like you have a great plan in place to reuse rainwater - kudos for the efforts.  

As for pump selection, if you can install the pump below the surface of the water in the tank, as you indicated with your reference to gravity feed, then an end-suction centrifugal is the booster pump of choice for a couple of reasons.  First, there is minimal priming to be concerned with since gravity will provide it for you and secondly, there are fewer friction losses effecting the suction line of the pump (i.e. no static suction lift in the equation)

There are a couple of things to consider when choosing a pump and selecting the correct size - flow & head.  How much water, in gallons per minute, does the irrigation system require to function properly and how much pressure (head) for proper operation.  Pump performance charts are available with all pumps to accurately select the proper one for each application.  When looking at pump curves, the X-axis indicates flow and the Y-axis indicates feet of head (1 ft head = .433 psi and 1 psi = 2.31 ft of head).  For this scenario, I'd suggest either a 3/4 HP or 1 HP pump, depending on the distance from the pump to your garden.

There are two manufacturers that have some great pumps for your application - Grundfos and Berkeley (Sta-Rite).  Grundfos has a very good 3/4 HP pump with a built in flow sensor and diaphragm - simply "plug & play".  It's the MQ 3-45.  Follow this link for more details - http://www.grundfos.com/web/homeca.nsf/Webopslag/PAVA-52JPUG

All the Best.

Tony