We have a 5 year old lemon tree in the ground here in Israel. It gets watered by automatic irrigation about 1/2" each day.
The many lemons that do grow on it are very dry and have brown areas on the inside of the fruit. The outside is also dry and has brown blotches that look as if it got sunburned.
Botanical Journeys Plant Guides Response:
If the dark spots affect the leaves as well as the fruit, I think you may be dealing with Alternaria.
Alternaria brown spot is caused by the Alternaria alternata fungus.
This disease has been found on citrus trees in Israel and in Florida. It leaves dark spots on the leaves which will usually be surrounded by a yellow halo.
It leaves dark, corky areas on the skin of the citrus fruit.
To control it, keep the lemon tree as dry as possible. Avoid overhead irrigation as water spreads the spores.
Even if you don't water overhead, the disease may continue to spread as even a heavy morning dew will provide it with the moisture it loves.
Also, daily watering may be too much. It will tend to promote excessive growth which will be weaker and more prone to disease.
If this is a problem every year, spray the tree with a copper fungicide every 3 weeks from spring until mid summer.
When citrus fruit is dry it is usually because the tree has received too little water while the fruit was developing.
This cannot be true in this instance.
I did not find a single reference to brown spot causing the fruit to be dry.
Not all lemons are equally juicy. For instance, the fruit of the Meyer lemon tree are exceptionally juicy while that of the pink lemonade tree is very dry compared to other types.
I wish you luck in restoring your lemon tree's health.