Water Your Plants Regularly
For tomatoes, it's really important to water consistently and thoroughly soak the roots. When the soil gets too dry, that's when you run into issues such as blossom end rot. Tomatoes also need water to pick up calcium from the soil. Be sure to give your plants about 2 inches of water per week through the summer.
There are several different options for watering. You can use a hose, wand, or watering can to direct water exactly where you want it. A soaker hose or drip irrigation system evenly and sufficiently waters your plants while reducing overall water usage. This also keeps the leaves dry by only watering the base of the plant, reducing chances of fungal infection. For low-maintenance watering, use a timer with your watering system and let it do the work for you!
It's also important to take into consideration the time of day you're watering. If you water in late afternoon or evening and the foliage gets wet, it's less likely to evaporate, which could lead to blossom end rot. If you do water later in the day, just be sure to water only the soil at the base of the plants and avoid water splashing the foliage.