I like my raita really thick ,if you want you can add some water to the raita to make it thin. If your curd tastes sour add 1 tsp sugar and beat it nicely. It will reduce the sourness. If you want to prepare the raita ahead, do all the chopping work and keep them ready and mix it just before serving. This way the raita would not become watery. You can even sprinkle some salt on the onions and leave it for some time, remove the extra water by squeezing and add then mix with curd and can be refrigerated until its use ,this way the raita will not become watery. You can add chopped cucumber in the recipe along with onions and tomatoes. Replace coriander leaves with mint leaves for a refreshing taste. For a south Indian version add a handful of grated coconut in the recipe.
Onion-Tomato Raita is the most common raita served with Pulaos and Biriyani .When I prepare south Indian style pulao or rice variety, I usually prepare the raita in south Indian style-with the addition of grated coconut. While the basic raita is just a mix of finely chopped vegetables with whisked curd and salt, one can get creative and prepare various vegetable raitas. Apart from Onion-Tomato raita, the most common raita varieties would be Aloo raita and Boondi raita. You can prepare raitas with the vegetables like grated beetroot or carrot or bottle gourd which tastes different from the regular ones or you can use greens like palak or mint for a healthy version of raita. You can even add few varieties of fruits like pomegranates, grapes and pine apple to raitas, check out the recipe for Anardana raita if you are interested. I prefer my raitas to be more thick and creamy as I am not fond of the watery and sour ones. Though the recipe is simple I would suggest you to go through notes where I have mentioned some tips for a good and delicious raita.