Over the past several months I have received e-mails and phone calls regarding how to safely dispose of pool water when draining or backwashing the pool.

There are two issues to consider: what is allowed by the Honolulu Department of Environmental Services if discharging into the public wastewater system, collection system or storm drains, and what potential damage may result to landscape plants if discharging onto your own property. Another consideration is whether the pool is fresh water or salt water.

Let's first consider discharging onto your own property. According to a fact sheet distributed by the Department of Environmental Services, it is always permissible to discharge onto your own property as long as all of the water remains on your property and is not allowed to flow into the storm drains or into neighboring properties. Most homeowners should choose this method to avoid the possibility of needing permits to discharge into public sanitary sewer systems.

If using your own property, the main consideration will be avoiding possible damage to the landscape plants. The main potential damage from a freshwater pool is the chlorine. Normal maintenance levels of chlorine will probably not cause much harm if the discharge is spread over a large area during periodic backwashing. If the pool has been recently super-chlorinated, wait until the chlorine concentration falls to normal levels, or below before discharging the water into the yard.

It may not be possible to drain the entire pool into your yard because of the huge volume that needs to be absorbed by the soil. Draining a typical 20,000- gallon pool into 1,000 square feet of yard is the equivalent of 30 inches of rain. Complete drainage will most likely require discharging the water into the storm drain or sanitary sewer system.

Saltwater pools present a more serious problem if discharged into the landscape. Chlorine is not used in these pools, so this is not an issue, but the salt concentration is similar to that of the ocean. When the roots of most plants are exposed to water with this much salt, they will become desiccated and the leaves will dry out and show severe burn symptoms. Some salt-tolerant plants may resist the damage at first but with repeated drainage of the salt water into the same area, even the most tolerant ones will eventually suffer severe damage or die. The only safe alternative for discharging salt water into the yard would be if the grass is seashore paspalum, but this should be only for periodic backwashing and the hose moved frequently to cover a large area then followed with a brief irrigation with fresh water. If saltwater pool owners are able to use their own yards, it is essential to make sure that all of the discharge is being absorbed on their own properties and not allowed to flow onto neighbors' yards or into storm sewers. However, as with freshwater pools, complete drainage will likely require discharge into the storm drain, or possibly the sanitary sewer, depending on your location.

Discharge of both fresh and salt water into the sanitary sewer or storm drain falls under the regulation of the Department of Environmental Services, and may require a permit, depending on the location. Chlorine levels should be less than 0.01 parts per million, and the water should be directed by a pump and hose directly into the storm drain, and not allowed to flow down the open gutter to the drain. The East Honolulu (Niu Valley to Sandy Beach) area allows both salt and fresh water discharge directly into the sanitary sewer.

The requirement of permits when using either the storm drain or sanitary sewer seems to vary with location. For more information, call the Department of Environmental Services at 768-3261 or 768-3262. For information about storm drains, call the Storm Water Quality Branch at 768-3245.

It would seem that in the case of freshwater pools, the easiest method of water disposal for ordinary back-washing is into your own yard after allowing the chlorine level to diminish. Saltwater pool owners have much more limited options, even with the backwash discharge. One possibility might be to install a French drain to allow the water to be dispersed into the ground without affecting surrounding vegetation. A simple French drain capable of handling the normal backwash volume of water can be built by installing a gravel-filled trench 2 feet deep, 2 feet wide and 6 feet long. This should be flushed with fresh water periodically to prevent salt buildup in the underlying soil.

In any case, please be considerate pool owners, and do not allow your backwash water to destroy your neighbor's garden.

Jay Deputy is an education specialist in landscape horticulture and turf at the University of Hawai'i-Mānoa Department of Tropical Plant and Soil Sciences, and state administrator for the Certified Landscape Technician Program sponsored by the Landscape Industry Council of Hawaii. Got a lawn care or turf question? Reach him at deputy@hawaii.edu.