Lemon can refresh hair and dry your hair out if not DILUTED enough. You can also try adding some oil or conditioner to counteract the drying effect. Be careful though, lemon WILL (Ok, last one for emphasis, I promise ;D) lighten hair in the sun.

If you want to avoid the lemon's drying effects and lightening, you could try other ingredients:
- Rosewater
- Diluted essential oils (lavender,rosemary, etc.)
- Tea
- Water + Oil to seal
- Aloe vera juice
- Honey + water (can lighten hair)
- Diluted vinegar (adds shine and smooths hair)
- Glycerin for moisture (careful, works both ways) preferably on humid days.