Yes, they should be watered at least twice a week. It's hard to over water aquatic plants, as they're partial to a damper than average environment. Whatever you do, don't let them go without being watered for long periods, they won't thank you for it. People often ask "how much water is enough?" and I always say more is better. In fact I've heard rumours that you can entirely submerge aquatic plants for extended periods and they will come to no harm.
I hope this helps with your question
Kind regards
Jimi