The waves can be big in Goa and are not suitable for all – check before you go in. Swimming is definitely not receommended during monsoon.
As with the rest of India, tap water is not safe to drink, but UV or Reverse Osmosis filtered water is fine. We use and trust Water to Go filter bottles which we travel with – buy one here.
I recommend sticking to hot food, served from busy stalls or restaurants. There are plenty of places to eat that are used to foreigners who prefer their curries a little less spicy.
Goa is generally a safe part of India but solo women should still do their due diligence, avoid wearing (only) swimwear while off the beach, and avoid walking on beaches alone at night.