A couple people on a weaving group I belong to asked some questions about live weight tension. I was unable to post photos on the group site, so am posting them here. I was describing where to attach the heavy weight and the counterweight.
On the above loom, my Leicester Dryad countermarche type, the back beam and warp beam do dual duty. The warp comes off the beam from the outside, so the heavy weights are attached to the outside end of the tension cord. This loom has 10# of weight on each side, counterbalanced with 2# and 4#. (I probably ran out of 2# weights.)
The Glimakra Victoria table loom has the warp coming off the warp beam from the inside of the loom, so the heavier weights go on the cord toward the inside of the loom. This loom has 13# of weight, counterbalanced with 2#.
This is a loom with another example of the warp coming off the beam from the outside. The heavy weights are on the outside cord.
I do not recommend using water bottles, milk jugs, or other thin plastic, since many are designed to break down after a time. I didn't know that until a couple milk jugs that I was using deveolped slow leaks. I stick with solid items or sand for weight now.