RALEIGH - In his book "Fooled by Randomness," Nassim Nicholas Taleb points out that rare, random events do happen, and often more frequently than we expect. I thought of Taleb when reading of one Raleigh Public Works Department official who thought the recent drought exceptional, the worst in 800 years. But who knew 2006 was year 799?

Although the drought, actually the third in six years, seems to be lessening its grip, we have yet to deal with all the lessons to be learned.

When the drought struck, Raleigh's water system had no margin of safety; there was no operable backup to the Falls Lake reservoir. Some neighboring water systems, Cary for example, have larger supplies relative to the population they serve. Or, like Durham, have connections to adjoining systems with capacity to share water.

We did have a connection to the Cary system, but it could only send Cary water. It couldn't bring water from Cary's more ample supply to us.

We have learned that, in an emergency and under the right conditions, the U.S. Army Corps of Engineers, which manages Falls Lake, can extend our supply by cutting millions of gallons per day from what it releases from the lake into the Neuse River. We also found that there is an outside possibility (requiring long bureaucratic study) that the capacity of Falls Lake could be increased. That capacity can be stretched further by building a planned system to reuse treated wastewater for irrigation. And finally, water from Lake Benson can be piped to the Neuse River, reducing the number of gallons that must be released from Falls Lake to maintain the river.

We are subject to frequent droughts, and relative to the growing population served -- even with the measures taken to extend Falls Lake's capacity -- our water supply is inadequate. This is hardly a surprise. It has been known for years.

In October 2000, the city put out a booklet called "Raleigh Trends." Discussing the water supply, it noted that "... a new 20-million-gallon treatment plant will be constructed at Lake Benson to meet needs after 2006." Actually, the Lake Benson project won't be ready until 2010. Two additional projects are planned through 2020.

Considering the precarious supply, we were not prepared with a well-designed plan to deal with our frequent droughts. The Raleigh City Council had to improvise conservation rules under the pressure of what looked like an impending disaster. As a result, businesses depending on water had to suspend operations or adopt expensive stopgap sources. Homeowners were subjected to confusing and changing water-use rules.

If our water supply is constrained, why did we add 135,000 customers from five adjoining towns to our system starting in 2001? Money, of course.

Raleigh plans to spend almost $700 million in the next 12 years to expand the water supply. Revenue bonds are being issued for the capital costs. The money to pay the bonds is being collected through water rates. More customers paying water rates that exceed the cost of day-to-day operation mean more money.

Since 2004, rates have been increased 9 percent a year. The bonds will be paid from these annual rate increases. Rates will double every eight years. Mayor Charles Meeker's aborted proposal for an immediate 50 percent increase would have just moved up those higher rates by five years. And the conservation measures adopted by users likely mean there will be a need for more than a 9 percent increase this year.

The result? Water bills are replacing real estate taxes as the largest payment to the city by more and more homeowners.

One reason is that there are costs on the water bill that should fall on real estate taxes. This practice started with the stormwater conservation fee. Previously such projects needed voter approvals for bonds to be paid from real estate taxes. Issuing revenue bonds paid by water rates to finance stormwater and water resource projects avoids the need for those voter approvals.

Water rates to finance the almost $700 million needed to build water supply facilities are a growing burden on every water user, rich and poor. Since a reliable water supply adds value to every property in the city, the burden would more fairly be allocated through the real estate tax.

Raleigh reasonably is planning "tiered" water rates next year. In adopting them, officials need to shift the burden of the capital costs from the water rates to real estate taxes. Water rates should cover mainly the operating cost of the system.

A safe, secure and adequate water supply is a fundamental responsibility of our city government. The costs of building that supply must be shared in the fairest way possible, through real estate taxes.

(Morton Lurie lives in Raleigh.)