My department has two 3000 gallon tankers and it seems to be the right amount for most jobs. Most of the area departments also have 3000 gallon tenders. We are only a rural department so this is why we have to. We house one in town and one is out at a subu station that is easy to go and get. Most of the reading that I have done says that if you have a 2500 gallon tender that your turnaround time is alot quicker than a 3000 tender because it takes less time to refill and empty. It is really up to your department on how many trips that you want to make. We usually only make the one trip out with ours because it is just about right even for a house fire. We roll up with a pumper with 1000 gallons and then a tender with 3000 gallons. Really depends on what truck you have know and how much water you carrry on them.
Do you have streams, ponds, and lakes which would be accessible? If so, you might consider a vaccuum tanker. We are about to recieve a 4000 gal tanker which refills itself in 3 1/2 minutes. It can be operated by a single person. It has a 4 person cab, 1000gpm pump which makes it capable of fighting fire and vaccuuming water at the same time. ISO also gives 100% credit in the tanker shuttle. Obviously not everyone needs or can utillize a large truck, so probably a 3000 gal is about the norm.
We have a 2200 gal, tanker from E-One. We have a neighboring department with a 3000 gal. I filled both of these tankers the other day at a structure fire and the time to fill the smaller tankers was quicker then the 3000. I know that there is only 1000 gal. differance, but I have to say that I like the 2000 gal. In referance to individual companies, I noticed that the 3000, and the second 2000 were Fouts Bros. The only thing that I didn't like about these was when they returned to the fill site they had 1/4 tank of water left. This was because they used the side dumps. The rear dump allows for all water to be dumped. This is the only thing I don't like the Fouts Bros. Tankers. I have no complaints about the E-One that we have. Other then these two companies I think that the other companies are similar.
We run a smaller tanker 2,000 gallons because of our roads and small drives. It is pump and roll with a 500GPM pump. We mostly use it for shuttle ops but occasionally pump the water off as we set up the dump site. The tanker follows our engine out with 1200 gal. We fill in just under two minutes at a fill site with the twin direct tank fills fed by and engine.
The only suggestions is if you shuttle water most of the time put direst tank fills on the rear of the apparatus at about waist height, ours are 3" with check valves and camlock fittings. All tankers in the 3 surrounding counties have agreed to do this and we maintain over 1100 GPM with a 5 mile round trip for our shuttle ops using 8 tankers.