Venice Public Water Bus: Alilaguna or ACTV

Yes, it is confusing. I will try to make this simple. If you arrive at (or have to leave from) the airport, you need either the Alilaguna or ATVO to get to the mainland, depending on where your hotel is.

For general travel around Venice and to the islands (Murano, Burano, and Torcello) you need the ACTV. You can buy a pass for 1, 2, 3 or 7 days.
https://quickvenice.com/transportation/actv-tourist-travel-cards.htm

The above post has confused me, but it's very simple:

• Alilaguna is a private ferry company that runs 3 lines of water shuttles from Venice Marco Polo airport to the floating part of Venice. They have several stops around the islands to let more people get on board. They use a color system to name their lines.

• ACTV is the City owned company that runs land and water buses in Venice. Water buses serve the 6 floating historic districts of Venice plus the Lido beach, Murano and Burano islands. ACTV water buses are nicknamed Vaporetti, but they work like the wheeled bus you use every day: they have designated stops, have different numbered lines, offer a night service and so on.
  ACTV land buses serve the mainland district of Mestre where many Venetians actually live. One of ACTV land buses goes from Marco Polo airport to Mestre railway station and Piazzale Roma Square; Piazzale Roma is basically a parking lot at the end of the causeway that connects historic Venice and Mestre. It's in front of Santa Lucia railway station and it is also the furthest point wheeled vehicles can reach before sinking.

ACTV and Alilaguna are two different companies. The 3 days ACTV pass can be used only on ACTV means of transport.

Note that you must swipe your pass every time you enter a boarding area, not just the first time you use it. ACTV loves collecting data and fines those that forget to swipe.

Darioalb provided a very good description of the 2 different water bus companies. Basically, you would only take an Allilaguna boat between the Marco Polo airport and the stop closest to your hotel. Daily travel amongst the Venice islands (and the Lido) would be on the ACTV vaporetti. The daily passes would only be used on the vaporetti. The boats look quite different and are well marked. The stops are also well marked, with very good signage. You are unlikely to mistake one for the other.

Just to confuse things a bit more.
As noted above, ACTV buses run from the airport to Piazle Roma in Venice. These are normal commuter buses, and you take your luggage on board with you. Costs 8 euro, makes several stops on the way to Venice. Runs every 20 minutes

There are also ATVO buses running from the airport to P. Roma in Venice. These are like a tour coach, your luggage goes underneath. Costs 8 euro, runs every 20 minutes, express to P. Roma.

So there is a bus every ten minutes, either ACTV or ATVO. We just buy tickets when we are outside the air terminal, selecting which ever bus is soon to depart.

The Alilaguna ferries are not so good for us. Slower than a land bus, and you do not get much of a view from them. But it depends a bit on your ultimate destination in Venice.

Thank you everyone for your replies. Your contribution helped me figure it out!! We are coming from the train station, so we are going to buy a book of 10 journeys as we are only there for 2.5 days. Our hotel is right at the San Stae stop (Hotel Al Ponte Mocenigo) and we prefer walking and getting lost so I think 10 journeys will work perfectly for 14e. We are going to Burano and Murano for a day, I assume the 10 journeys will cover it but will kick in for an extra if we need to. We return to the train station on Monday so we will be fine with ACTV.

Thanks again!

Steven

Vaporetto does no sell a book of tickets; you buy a pass (a card) which is good for a certain length of time - one day, two days etc. Every time you get on the boat, you validate it by touching it to a machine on the dock. The pass is not effective until the first time you validate it and the machine will reject it when your time has run out. You can use your pass as much as you like during the period it is valid. In a way the vaporetto works on the honour system as no one actually takes your ticket when you get on. But there are random checks when you are on board and woe betide you, I imagine, if you do not have a valid pass/ ticket!

https://europeforvisitors.com/venice/articles/local-transportation-index.htm
This link should also explain it all easily.
This site has tons of great information about other things in Venice, too.

The 1.40 euro per ride, ten ticket deal is only available if you buy a Venezia Imob card, which costs 50 euro. Once you have the card, you load it with trips.

Good value if you visit Venice frequently or for an extended period, and that’s why I have a card. After about eight or nine trips, the pass pays for itself, compared to the usual seven euro cost for a single ticket. But not such good value if you are only staying for a few days. In that case, a 24, 48 or whatever time based pass is better value.