Pressure
Tank
Motor
Pump
Intake
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Choosing a Pump for Rainwater Harvesting
Introduction
Water harvesting is the practice of cap­turing rainwater runoff, normally from a rooftop, and storing it in a tank or cistern for use around a home or busi­ness. While gravity flow from a cistern is generally enough to fill a bucket or to water a few nearby plants, most wa­ter-harvesting systems require a pump to convey the water from the holding tank to the spot where it will be used (Figure 1). Typical uses include water­ing plants, washing vehicles, flushing toilets, and washing clothes. A pump can increase the uses of the water-har­vesting system and is required when consistent pressure is needed. Knowledge of how pumps operate and how they are selected will ensure that an efficient and appropriate pump is included in the wa­ter-harvesting system design.
Because pumps and plumbing sys­tems are diverse, people installing wa­ter-harvesting systems should consult an experienced plumber to make sure all ap­plicable codes are met and that there will be no damage to the pump or plumbing. Pump selection should be based on the flow and total head the pump is required to supply. Flow is the rate at which water travels through a pipe and often is mea­sured in gallons per minute (gpm). Total
Figure 1. Pump with pressure tank before installation and example of system in use
Cistern