My 9month LO recently 4-5days only poop once. Is it normal? Consider serious constipation? She is breastfeeding and solids now. I will give her water after solids (about half cup of water each day). Is it enough? as breastmilk contains lots water too.

Hmmm doesn't sound like constipation. Have you fed baby anything new recently. Sometimes if there's something new, baby's system will take time to get used to it and this could be the reason why baby is taking a while to poop. What kind of solids have you been feeding your little one? Maybe if you included more greens and fibre, it will help move things along down there. Reckon that as long as baby is not showing pain or signs of discomfort, all should be well.