The tourist Tax in the territory of the Municipality of Venice official version available here
The tax must be payed cash on the arrival and it's not included in the apartments' rental quoted at VeniceApartments.ORG
You can find the right amount of the tax in the apartment's page; usually the tax amount for the VeniceApartments.ORG apartments is 1,50 (see below) or 0,75 Euro (in the other periods) per person per night
- max 5 nights per stay (starting for 6th it's free) - children under 10 years of age no tax; 10-16 years 50%
periods with tax 1,5 Euro in 2012: -from the 1st to the 8th of January -from the 4th to the 22nd of February -from the 1st of April to the 31st of October -from the 3rd to the 9th of December -from the 23rd to the 31st of December