Both deca and test are known to cause a lot of water retention. Truth be told though, if you are using the proper support supplements with your cycle, the water retention won't be too bad at all.
Remember to include the proper support supplements with your cycle:
1. An AI to keep estrogen in the low-normal range. Aromasin at 10mg EOD is a good dosage.
2. An anti-prolactin drug to keep prolactin in the low-normal range. Cabergoline at 0.25mg EOD is a good dosage.
The support supplements are very important because high estrogen and prolactin levels can lead to side effects like gyno and water retention.
Sodium is an extremely important electrolyte needed for muscle contractions. You don't want to consume an excessive amount of sodium but you don't want to eliminate from it your diet completely either.