If and when Watertown city workers begin inspecting rental properties, they're more likely to find no one to answer the door than a decade ago.

The Census Bureau's most recent data show the city's rental vacancy rate rose 63 percent in the past decade. Watertown had 818 empty rental units - mostly downtown and in the area surrounding it - when the census was taken last year, compared to 503 vacancies in 1990. Those 315 additional empty units left the city with a rental vacancy rate of 11.5 percent in 2000.

By comparison, the state's vacancy rate for rentals dropped from 4.9 percent in 1990 to 4.6 percent in 2000.

Owner-occupied housing in the city is also on the decline.

The Census 2000 housing data for Watertown come as city officials ponder Watertown's quality of life and whether to register and inspect rental units. The data also show that Watertown's population dropped 9.3 percent from 29,429 in 1990 to 26,705 in 2000.

Despite the population drop, city property owners opened 377 more rental units in the 1990s, whether in new buildings or, more likely in many neighborhoods, by splitting up homes or renting them out. The jump in rental properties comes well after most Fort Drum expansion swept through the north country in the late 1980s.

The Census Bureau compared all housing as well as pared-out rental units and owner-occupied housing, which could include houses, mobile homes and even apartments as long as they are owned by the occupants. Vacancies were determined by information from landlords, owners, neighbors, rental agents and others.

Combined vacancies for both homeowners and renters increased 45 percent in the past 10 years, from 975 in 1990 to 1,414 in 2000. At the same time, there was a net increase of 45 housing units available in 2000 than 10 years earlier.

Overall, Watertown's vacancy rate for both rentals and home ownership rose to 11.4 percent of the 12,450 housing units reported in the 2000 census. There was a 7.9 percent vacancy rate in 1990 when there were 12,405 units.

The state's overall vacancy rate remained constant at 8.1 percent during the 1990s, but that figure was inflated by an average 3 percent vacancy rate in vacation and occasional-use properties. Watertown has few of those and most were occupied.

Overall, the data show a clear shift in the city from homeowners to renters and a rise in vacant housing, especially rentals.

The city had 6,737 rental units in 1990 compared to 7,114 rental units in 2000. Rentals with people living in them went up by only 1 percent, from 6,234 in 1990 to 6,296 in 2000.

At the same time, the city had 5,288 homeowner units in 1990 compared to 4,963 in 2000. Housing with owners actually residing in it dropped by 9 percent, from 5,196 in 1990 to 4,740 in 2000.

It represented a homeowner vacancy rate that grew from 1.7 percent in 1990 to 4.5 percent in 2000.

The state's homeowner vacancy rate dropped from 1.9 percent in 1990 to 1.6 percent in 2000.

Watertown's shift from homeowners to renters is nowhere more apparent than the city's downtown census tract, listed as "Tract 621" on census maps, which is also the most populated. It has the Black River on its northern border, extends west to Massey Street and then cuts diagonally to Washington Street south to Flower Avenue East and then northeast to Central Street.

Owner-occupied housing there dropped 17 percent from 503 units in 1990 to 419 in 2000. Renter-occupied housing rose 12 percent from 1,544 in 1990 to 1,728 in 2000.

At the same time, the area has the city's highest overall vacancy rate of 15.5 percent. The most populated tract in the city, it had 175 vacant rentals reported in 1990 compared to 267 in 2000. There were another 16 vacant houses for sale in 1990 compared to 27 in 2000.

Downtown's rental vacancy rate of 13.4 was overshadowed only by the city's northeast tract, "Tract 613," which had 16.5 percent of its rental units vacant in 2000. It has fewer homes and a smaller population, which dipped from 3,508 in 1990 to 2,688 in 2000.

Vacancies for rent in the northeast sector grew from 34 in 1990 to 103 in 2000. The sector had seven vacant houses for sale in 1990 compared to 35 in 2000.