Grace Episcopal Church and Presbyterian Student Center Foundation appeal from a judgment upholding the City of Madison’s levy of special charges for maintenance of the State Street Mall/Capitol Concourse. The appellants are religious institutions exempt from general property taxes under sec. 70.11(4), Stats., and they argue that the maintenance charge is a general property tax. They also argue that the maintenance charge does not satisfy the requirements for a special charge under sec. 66.60(16), Stats., and is arbitrary, unreasonable and discriminatory. We conclude that the city properly enacted the charge and that the appellants are subject to it, and therefore affirm the judgment.
The State Street Mall/Capitol Concourse was constructed as a special street and sidewalk improvement *334in downtown Madison during the 1970's. To help defray the costs of construction, the city established an assessment district and assessed capital improvement costs against properties benefited by the construction. The appellants are located in the district and paid their assessments without protest.
The city originally paid all costs for maintenance of the new Mall/Concourse. Maintenance included lawn, tree and shrub care; snow removal from walks and crosswalks; trash clean-up and removal; and bus shelter and fixture maintenance. In 1981 the city created the State Street Mall/Capitol Concourse Maintenance District to assess a portion of these annual costs against property owners adjacent to or near the mall. The city pays two-thirds of the maintenance costs and allocates the remaining one-third as "special charges” to property owners including the appellants. The appellants commenced this action to challenge the city's levy.
The appellants first argue that the Mall/Concourse is a citywide improvement which must be supported by general property taxes. They argue that charges to maintain the improvement are therefore general property taxes that cannot be levied against their tax exempt property. We decline to consider the nature of the original Mall/Concourse improvement. That improvement is not at issue here. Adjacent property owners paid one-half of the original construction costs by special assessments. The appellants paid their assessments and did not contest the assessments' reasonableness or their special benefits from the project. Those arguments are now foreclosed. We will only consider the nature of the maintenance services rendered by the city and whether they fall *335within the exception to general property taxes permitted by sec. 66.60(16), Stats.
Section 66.60(16), Stats., provides that "special charges for current services rendered may be imposed by the governing body by allocating all or part of the cost to the property served." Current services "include, without limitation because of enumeration, snow and ice removal, weed elimination, street sprinkling, oiling and tarring, repair of sidewalks or curb and gutter, garbage and refuse disposal, sewer service and tree care." Id. Most of the special maintenance services performed on properties in the Mall/Concourse area are specifically enumerated in sec. 66.60(16), including snow and ice removal, garbage disposal and tree care. Before construction of the Mall/Concourse, the appellants and other property owners in the area were responsible for this maintenance, and as the trial court noted, it would otherwise have to be done by appellants' custodial personnel. The appellants do not argue that the property owners' one-third share of annual maintenance costs does not reasonably correspond to services specifically enumerated in sec. 66.60(16). We conclude that special charges for one-third the cost of Mall/Concourse maintenance is appropriate under sec. 66.60(16) and not a hidden general property tax. As a special charge rather than property tax, the appellants' exemption under sec. 70.11(4), Stats., does not apply. Yates v. City of Milwaukee, 92 Wis. 352, 357-58, 66 N.W. 248, 249 (1896).
The appellants argue, however, that even if the cost of services enumerated in sec. 66.60(16), Stats., can be passed on to property owners, special charges cannot be made on a district basis. The appellants would limit sec. 66.60(16) to permit special charges for iso*336lated work directly provided to a particular owner's property. This argument requires the interpretation of sec. 66.60(16).
The meaning of a statute is a question of law which we decide independently of the trial court's conclusion. State v. Denter, 121 Wis.2d 118, 122, 357 N.W.2d 555, 557 (1984). The primary source of construction is the language of the statute itself. Id. at 123, 357 N.W.2d at 557. The rules of construction are used only to determine the meaning of an ambiguous statute. State v. Tollefson, 85 Wis.2d 162, 167, 270 N.W.2d 201, 203 (1978). That the parties disagree concerning a statute's meaning does not render it ambiguous. A statute is ambiguous only if reasonable persons could disagree as to its meaning. Kollasch v. Adamany, 104 Wis.2d 552, 561, 313 N.W.2d 47, 51-52 (1981). Whether reasonable persons could disagree is a question of law. St. John Vianney Sch. v. Janesville Ed. Bd., 114 Wis.2d 140, 150, 336 N.W.2d 387, 391 (Ct.App. 1983).
Section 66.60(16), Stats., is not ambiguous. Although the statute must be strictly construed, The Oshkosh City R. Co. v. Winnebago County, 89 Wis. 435, 437, 61 N.W. 1107, 1107-08 (1895), nothing in sec. 66.60(16) indicates that it is limited as the appellants contend. Several of the enumerated services, such as street sprinkling, oiling and tarring, are unlikely to be performed on an isolated basis to individual property. Others, such as snow and ice removal, refuse disposal and tree care, can be reasonably performed on an area basis. We cannot conclude that the services rendered must be isolated. Nor can we conclude that the maintenance charge must be levied on an individual rather *337than district basis. Because the maintenance can be performed on an area basis, it is only reasonable that the expense be divided among properties within the area served.
The appellants rely on the statute's reference to "the property served" to support their contention that charges cannot be imposed throughout a district. We disagree. A statute's reference to "property" includes the plural form "properties." Section 990.001(1), Stats. Consequently, all or part of the cost of current services may be imposed on the properties served. The city's maintenance district is composed of the properties served by the maintenance. The district approach to allocation is not improper.
The appellants also argue that their properties are not specially benefited by the Mall/Concourse maintenance. Special assessments under sec. 66.60, Stats., must satisfy two substantive requirements: (1) the assessment must be reasonable, and (2) the property assessed must be shown to derive special benefit from the assessment. In re Installation of Storm Sewers, 79 Wis.2d 279, 287, 255 N.W.2d 521, 525 (1977). The charges for the services provided here are not special assessments under sec. 66.60, but rather are special charges as provided for in sec. 66.60(16).
We conclude that the city need not show a property's special benefit before imposing special charges. The. court in In re Installation of Storm Sewers relied on sec. 66.60(3)(d), Stats., in deriving the requirement of a special benefit. In re Cherokee Park Plat, 113 Wis.2d 112, 117, 334 N.W.2d 580, 583 (Ct.App. 1983). Subsection (3)(d) is one aspect of the report required by *338sec. 66.60(2) and subsec. (2) is not applicable to proceedings under sec. 66.60(16). Section 66.60(16)(c). To comply with sec. 66.60(16), the municipality must establish that current services of the type described in the statute are rendered to the property or properties sought to be charged.
Lastly, the appellants argue that the charges are arbitrary and capricious because their religious properties are included with commercial properties in the district. The appellants have failed to show, however, the arrangement's arbitrariness. The appellants have not shown that commercial properties on the Mall/Concourse require greater maintenance than their properties. Both the appellants and the commercial property owners are being relieved of maintenance that they previously performed and which they would otherwise be responsible for. The joinder of appellant's properties and commercial properties is not unreasonable or arbitrary.
The appellants also contend that they are being arbitrarily charged to maintain a city park while other parks are maintained by the general tax levy. This is simply a repeat of their first argument that the Mall/Concourse is a citywide and not a local improvement, and the argument fails for the same reason. The Mall/Concourse, unlike the city parks referred to in their argument, was financed in part by a special assessment. The appellants had and passed up an opportunity to contest this assessment. The Mall/Concourse, therefore, is sufficiently distinct to merit special charges for its maintenance.
By the Court. — Judgment affirmed.