Case Study - Biscayne National Park
The Federal Energy Management Program (FEMP) assisted Biscayne National Park in evaluating a reverse osmosis (RO) water system design at Biscayne National Park on Adams Key. The National Park Service (NPS) would like to have a constant potable water supply on Adams Key, which currently draws potable water from a cistern.
The NPS is considering the addition of an Environmental Education Center to Adams Key. If this camp were to be built there, the potable water use is estimated to increase an average of 1,800 gallons per day, based on usage at a similar camp that exists on a near-by key.
The study evaluated the current water usage including plumbing and other on-site uses on Adam's Key as well as the potential to have an RO system adapted to the cistern, the potential for water to be pumped from a saltwater well and treated via RO, and the possibility of increasing storage capacity of the current rainwater collection system.
Recommended Measures
For the situation where an environmental education camp is not installed at Adams Key, Installation of a reverse osmosis system is a very costly way to increase water system security. The least expensive route would be to install state-of-the-art water efficiency measures and increase the storage level for the rainwater system.
Based on the literature, the analysis, and the track record of reverse osmosis systems and water efficiency equipment it is clear that installing the water efficiency equipment and increasing the capacity of the rainwater storage system is the best way option for Biscayne National Park at this time. This approach will save on the labor needed to test the water from a reverse osmosis system and the labor to maintain a reverse osmosis system. The efficiency equipment will be relatively easy and quick to install.
For the situation where an environmental education camp is going to be installed at Adams Key, installation of a reverse osmosis system would be necessary. Based on water usage of a similar camp at Elliott Key, it is estimated that this camp would use 1,500 - 2,000 gallons per day. While it is hard to determine the actual sizing needs for the RO system for the camp without seeing the plans for the camp, it is clear that an RO system would be needed. It is estimated that with this situation the site would need an RO system capable of delivering between 1,800 and 2,200 gallons per day. It is recommended that during the design of the camp that efficiency measures and rainwater collection be considered to allow for downsizing the RO system.
In addition to the larger RO measure, a variety of other measures were recommended. The bathroom faucets have flows of approximately 2 gallons per minute (gpm). These faucets could be retrofitted with aerators that have flows of 1 gpm. The washing machines in the homes were estimated to use between 35 and 40 gallons/load. There are a number of washing machines that use less water per load. There is at least one model on the market, which uses approximately 15.8 gallons/load. It is estimated that the dishwashers at the residences use approximately 9 gallons per load. It is recommended that they be replaced with models that use 5.5 gallons/load or less.
One of the hose bibs was found to have a leak during the walk through and it was related that at one time a hose had been left running accidentally. This could possibly deplete the potable water supply.
It is recommended that the measures above be undertaken along with adding about 2,000 extra gallons of storage. It is estimated that the measures would have a cost of approximately $4,500 for the efficiency measures and $1,500 for the extra storage capacity. Table 1 describes the current water usage from the water-using equipment and the expected usage after water conservation measures have been implemented.
Table 1: Current and prospective annual potable water usage, both residences
| Current usage (gallons) | Proposed efficiency measures | Proposed annual usage (gallons) | Estimated savings (gallons) | Estimated installed cost of efficient appliances ($) | |
|---|---|---|---|---|---|
| Bathroom sinks | 5,600 | Faucet aerators | 2,800 | 2,800 | 10 |
| Washing machines | 31,500 | Install high-efficiency washing machines | 13,160 | 18,340 | 3,600 |
| Dishwashers | 7,280 | Install high-efficiency dishwashers | 4,480 | 2,800 | 800 |
| Leaks | 2,800 | Fix all leaks at hose bibs ($40); add shut off nozzles at hose bibs ($50) | 0 | 2,800 | 90 |
| Other appliances | 57,320 | No change | 57,320 | 0 | --- |
| Interior gallons total annually | 104,500 | 77,760 | 26,740 | 4,500 | |
| Total monthly usage | 8,708 | 6,480 | 2,228 |
Other Equipment
Improvements to the following equipment were considered, however, no cost-effective water efficiency opportunities were found. Irrigation system: Training and software are available that will allow a landscape irrigation person to schedule watering based on local evapotranspiration (ET) weather data, plant needs, and soil requirements. Expected savings from this approach are minimal because it would only apply to the lawn area, which is very small.
Recycling water in dishwashers, cart washers, and washing machines: All the dishwashers, cart washers, and washing machines already recycle water.