Water Treatments are often confused with the phrase water proof or water proofing. The truth is, over time, fabric weave and meshing stretch and when that happens water finds the path of least resistence, like air to make its' way inside.
To prevent this we perform water treatments. On weaker blankets, sometimes a double application is required to enable the best possible protection. With that in mind, this does not always mean the blanket is "water proof". This is where the misnomer happens. A treatment is very different than water proof. Age, wear and tear and even on new blankets, stretching (as mentioned) can play a big factor in how effective a treatment is.
Although it is not necessary, we recommend having your outdoor blankets water treated when you have them processed every second cleaning. We also recommend getting all repairs needed in a blanket to bring fabric back together to allow for a stronger bond when treatments are applied.
This will allow you to prolong the water treatment life between washes as well as the life and integrity of the blankets themselves.
Water treatments are meant to keep water out, as best as possible. It does not mean that it will STOP all water from penetrating the blanket, rather, it is a preventative measure.